Nah, it's not just you Timothy. It sounds cool to me too.
I think you could make a case for a Divine Mystery religion of Isis Myrianoma (as great mother/supreme creator) and even the Mongolian Tengri (sky god/creator) as being Divine with a similar sort of construction.
Imagine if the Mongol shamans were holy companions with Purity / Transcendence / Intervention instead of just diabolic summoners?
Cheers,
Lachie
First off, thank you for responding here. I really appreciate it that you are willing take time for these forums. Your comments have clarified for me many of the things that I didn't, at first, understand about this edition.
I must not have presented my idea very well. My idea was to have the Realm modifiers (as presented in Ars Magica 5th edtion) act as a kind of magic resistance, not actually be magic resistance in the usual sense. Basically, when in a foreign aura a power would need to have a penetration score equal to the Realm modifier plus any actual magic resistance of the target to have any effect. Just like normal magic resistance, personal range effects wouldn't need to penetrate. This would allow a wide range of effects to function without penalty while still providing a defense against most offensive effects.
As for it devaluing Parma Magica, I don't think that it would. The added resistance would only work in foreign auras which would be a severe restriction to magi. It is limited in effectiveness. Most Divine auras, for example, do not provide enough protection to save a mage from magical attack. Finally, it would not have any effect on the negative social effects of the Gift. In my mind, this aspect of Parma Magica is at least as important as the actual magical defense that it provides.
In short, Parma Magica is still incredible. As you say, "Wow"!
Creatures having similar problems to mages without unbalancing the rest of the game is not a bad first step... 
I agree with your assessment of the fundamental problem of balance and I appreciate the magi-centered view of the game. I was just hoping to find at least a partial solution to the "why doesn't the Dominion protect normal humans from demons?" question without changing the "magi at the center" orientation.
Sit vis vobiscum,
ShopKeepJon
The dominion does protect normal humans from demons, etc. Just not directly, by the level of the aura, but by Faith points.
True Faith gives you Magic Resistance equal to Faith Points x 10.
Normal people (those who don't actually have True Faith) can temporarily acquire Faith Points by wielding relics. Most cathedrals/monasteries will have some relics, so by presenting these relics to demons normal people (or at least clergy) can protect themselves from demons --- particularly if they are also in a divine aura which will both penalise the penetration of the demons and boost the magic resistance provided by the relics.
Also, from memory, there are rules in the Divine about people acquiring temporary faith points (and hence magic resistance) by participating in various church ceremonies (getting blessings etc).
Yes, but none of the people you mention are "normal" humans. The run-of-the-mill believer who should expect some sort of protection from demons while within the Dominion.
Of course, extraordinary people (True Faith) or those in extraordinary circumstances (possessing a relic or having participated in special ceremonies) can have protection, but what about the vast majority of people for whom the Dominion is no help at all?
I don't think that it is unreasonable for a normal believer to expect to have some protection from the "powers" of demons while living and worshiping in a Christian community. If they fall to the wiles of a demon, well that's another matter...
Sit vis vobiscum,
ShopKeepJon
I agree with you. I think this is where saints can greatly contribute to the setting. A saint has powers that it can use to protect people, and can actually fight demons and drive them away. There are special days where that saint might be especially active, making an interesting story, and saints have special patronages so that a particular saint might be more likely to manifest in response to a particular threat.
I like that it's possible for faeries and magical creatures like ghosts to live in a Dominion aura. And demons too -- there are lots of things in cities that demons should be drawn to, lots of opportunities for sin. Just being in a city shouldn't protect you against their wiles.
Enchanting Music, unless it's Divine in origin, just isn't as enchanting within the Dominion. You do much better taking the person you want to enchant on a picnic in the wilderness first, or waiting until nightfall. In the bright light of day, and within the range of the church bells, many people think that supernatural powers like Enchanting Music don't work, and the evidence would seem to support them in this. 
This is very good! I'm going to have to put more effort into local saints...
No, but I like the idea of it protecting you from their powers. What they do with trickery and a persons own corruptible nature is another story.
My suggested "resistance" did not affect personal range powers specifically so that faeries and demons could live within the Dominion. (And to allow powers like Second Sight, which explicitly doesn't usually have to bypass resistance, to work.)
I'm increasingly leaning this way. It seems to make a lot of sense in the setting. Just make sure that all of the players are aware of this limitation on Supernatural Abilities when they are creating their characters...
Sit vis vobiscum,
ShopKeepJon
except that only a minority of individuals have any Magic Resistance (typically the few with True Faith or a Relic). If you have no MR, then so long as the skill roll succeeds, the Music works. Only if they have to Penetrate MR do they have really serious problems...
OK, it's harder to make even the basic skill roll, but the lower effect target numbers (eg 9+) aren't that hard to achieve, even with penalties. (And not if you have any serious chance of the higher target numbers when in a favourable aura!)
We decided to try an experiment for our current saga. We all like Mythic Europe, and I thought it would be fun to explore it through the eyes of a mundane, rather than through the regular perspective of a magus. Another player suggested that all the characters be Redcaps, working for the Order but ignorant of its exact magical formulas and powers. Some thought a typical companion might be too wimpy, so we opted to create mythic companions, a middle ground between my ultra-low fantasy idea and the usual fantastic nature of our sagas.
I had some ground rules. No one could have magic resistance of any type. The mythic companions had to be constructed by the rules in HoH:TL, meaning they have to have Blood of Heroes and a personality trait that the storyguide can "steal". Or, they had to use a mythic companion from another supplement. One player wanted to do more with faerie, and since the Realm of Faeries isn't out yet, we jury rigged some rules for him based on other mythic companion rules. Everyone should have a Supernatural Virtue or some mythical power derived from their bloodline, but no "super hero" effects: invisibility, flying, or teleporting. No one could be mock-Gifted, meaning no negative social modifiers that would keep them from interacting with mundane society.
We set the game in 1240, after the Albigensian Crusade and during the Medieval Inquisition. We also invented a catastrophic event in the Order's history that would warrant four or five Redcaps working together, rather than the single canonical traveler. Essentially, we took what we liked, ignored what we didn't need, and invented a background for the saga we wanted to play. That's what everyone does, right?
It's been about six months of regular weekly playing, and it's awesome. We've avoided the rapid power escalation that starting magi seem to always go through. Without magic resistance, our characters are susceptible to all sorts of minor mythical creatures. The Might 5 leprechaun with his annoying power to make a character dance really is annoying, not just another Perdo Vim target/trophy.
We like that our Supernatural Abilities work best out in the wild. We haven't changed the Realms Interaction Chart at all. We are at a disadvantage in town, which has become a role-playing advantage. We can't just entrance the local priest to do what we want him to, but now have to engage with him socially. Instead of seeing the Realms Interaction Chart as broken, I see it as helping to push weirdness (folks with supernatural powers) to the margins of society.
So, our saga might not be everyone's cup of tea, but we didn't make if for everyone; we made if for us. It has some very nice constraints that keep it low-powered (not necessarily low fantasy, as we've encountered several fantastical elements in the sessions). Abilities increase much slower than Arts, so while some characters might have awesome Supernatural Abilities, they aren't going to increase to god-like awesome anytime soon. And because they are Abilities, they are limited by a character's starting age. No Perdo 20 starting characters here! No Perdo at all, in fact. Not for everyone, again, but good for us.
So, in conclusion, we find that Supernatural Powers are nicely balanced as Abilities, with a nice starting range that allows us to affect stories but not, usually, to "derail the train" with them. The Realms Interaction Chart works just as well with them as with Arts, even better we think, since with Arts and maybe vis a magus could still hurl a fireball in a cathedral. That might be your Mythic Europe, which is fine, but it's not ours.
happy gaming,
Matt Ryan
Given that the average Divine aura within a city is 3, Supernatural abilities within a city have, on average, a -9 penalty. Do most of your characters consistently roll 18 or more for their Enchanting Music?
That's 18 or more for the lesser effects of Enchanting Music...
Now I'm not saying that this is necessarily a bad thing. In fact, I think that such restrictions can be good for role-playing. It's just that I don't think anyone can say the penalties to Supernatural Abilities are insignificant.
Sit vis vobiscum,
ShopKeepJon