I suggest "Somewhere Else" only because the Theban Tribunal is already well documented and focuses on older traditions than Rome. One of the other provinces would more likely contain untouched Roman secrets. There needs to be reason why the Roman sites were lost. On the fringes of the Empire, Rome's hold was more tenuous and more likely to have been lost by invaders and people uninterested in preserving Roman traditions. Byzantium is a continuation of the Roman Empire, they have maintained many of its legal and cultural traditions for hundreds of years.
Some suggestions would be Iberia (favorable – long Roman tradition and many invaders to cover it up; unfavorable – frequent location of other on-line sagas); Rhine – (favorable – Teutonic forests with lost legions and etc, changing borders; unfavorable too much gild and covenant politics); Provencal (favorable, ignored location, many Roman sites lost to dark age invaders and late feudalism, good ruins aqueducts and forums in several towns, dangers of the Albigenisan Crusade always in the background; unfavorable – no core book and not very exotic); Loch Leglean (favorable – farthest Roman outpost, clear roman presence with few Roman roots, history of a missing legion, 2 walls and lots of forts still around, Tribunal not generally friendly to Roman Magi or scholars for interesting stories; unfavorable – another popular online saga location, might be hard to stay focused on “Rome”).
My first choice is Scotland (my last table top saga was set here but it didn’t get enough interest among local players). Second choice is Provencal. Third choice is Rome.