A small soffit for a few feet is not going to radically mess up your room acoustics, unless you're unlucky and end up sitting just where it creates a direct reflection. Building a second soffit might make sense for appearance reasons, but it probably isn't acoustically necessary.
Rooms with low ceilings sound "different" than rooms with taller ceilings. A low, drop ceiling with insulation above it absorbs a lot of bass (a good thing), but can sound "cramped" and dead. While I'm normally all for this approach, if the ceiling ends up 6'6" off the floor or less, don't do it. Especially with tall, or high-mounted speakers. You can get reflections off the ceiling (even with acoustic tiles - the angle of incidence is very low) and things get jumbled.
If building soffits is no problem, you can build a shallow network of them and give them soft (cloth) sides, and put insulation inside them. It's the sort of thing you want to plan out carefully, but it helps a lot with bass control and isn't as invasive as a typical dropped ceiling. More cost and effort, though.
Soffits are nice; you can hide wiring in them, use them for sound trapping, shaped sound reflection, and they make a room more interesting.
