Acoustical Instruments - a Bad Idea??

I can’t speak to all situations, but I have an upright piano about 20 feet from my audio system and I’ve never noticed a problem with it “singing along.”

Strings by themselves shouldn't be much of an issue.  Now instrument bodies, like an acoustic guitar, violin, upright bass, any kind of drum, or a piano, those can be problematic.  The issue isn't the strings as much as the resonance cambers of the instruments. They don't care where the sound energy comes from (strings or from the speakers across the room).  The energy is going to enter the resonance chamber, bounce around inside, get changed around, and then dumped back into the room.

My experience is, probably not a problem, but easy the throw a blanket over if need be...