Consider Performance Magic (Mysteries and Societates - Jerbiton).
You can use the Duration: Performance, which is equivalent in power to Concentration. For those who haven't got those books, the advantages of this is that A) you can disguise magic as other activities (like music) and B) you don't have to roll for Concentration while doing it. IIRC
But what about making devices? Could one make say a magic lute, with a Muto Imaginem effect Duration:Performance??? Once played, the effect keeps on going as long as the music does. Legal or not?
And how would one use the InVi guidelines about detecting magic? Once the magic is over, it deteriorates in "effective magnitudes" when the original duration has passed again. But what is this for Performance? Would it count as Diameter, because this is the same 'power level'???
A musical instrument would still be limited to individual "performances", which I don't think(?) are "a 4 hour concert", but separate pieces, if possible quite long ones. So that adds "uses/day" onto it, infinite if you want a magical lute that just "always works".
But if they were magical turntables, I could keep the beat going constantly for many hours as a single "performance" playing old school Chicago House music.
Who needs a light show? I can use Imaginem and Ignem to generate the lighting effects with my magical decks! Add to that a Rego Mentem effect, and I have an army of clubheads to do my bidding! Muahahahahahaha!!!!!!
Of course, they are all drunk and/or drugged up, so it wouldn't be the most efficient army