To be honest, the Bose system is not necessarily your best choice if you ARE looking for a stereo experience for your audience (it'll be pretty good for you, though). But the whole POINT of the Bose system is to shove out a planar waveform, and produce an even, non-localized sound all over the room.

Stereo, OTOH, works best with systems that DO localize the sound source, so that L & R sources are better defined.

Technically, the only true way to A/B a mono system and a stereo system is to go between a mono PAS playing mono, and a stereo system playing stereo. Putting mono through a two speaker system is going to introduce phase artifacts, and volume differences need to be very carefully aligned.

The thing which tips the balance, for me at least, is how poorly many arranger's true stereo sounds (from stereo samples, NOT mono samples panned around the field) collapse to mono. Yes, in fairness, IF they did collapse without going phasey, mono would be a decent alternative, especially for larger or irregular shaped venues, but I can hear it pretty plainly on a LOT of stereo sounds. It isn't the same sound in mono. It is hollow and phasey and just not the same.

Fix that, and things are far more even in the choice. There is a HUGE difference in sound between a stereo sound, played in stereo and listened to so far away that it can no longer be discerned as stereo, and a stereo sound that is collapsed to mono internally, and played through the one speaker. Phase issues are so much more apparent using the latter scheme.

Primarily, this effects our stereo piano sounds, but I can also often hear a big difference in the sound of the effects themselves, reverbs sound pinched, choruses get weird and phasey, Leslie sims go all electronic sounding, etc..

There's a reason there is a MONO button on any decent recording console, or on most of our DAW's. Checking that your sound isn't going to change radically when you listen to it in mono is a basic part of mixing. It is a shame that few designing arranger sound sets (and some WS's too) and effects structures seem to be aware of this necessary step...