What room treatment product have transformed your room or audio system?

interesting topic. I have my wall behind my speakers treated and the  room has carpet and furniture. it also has a 1 ft. soffit from the ceiling that divides the room in half that faces the speakers.  should I be treating the flat surface of the soffit also?

Frame the soffit with an angle finish in drywall and taper with a radius into the flat of the ceiling Tom

Some interesting products mentioned! I haven’t thought of digital room control before.
I’ve been listening and adjusting the past few days and have gotten to the point where I’m really satisfied, a combination of panels, bass traps, diffusers, and hybrid products.

 here's what I did for a start on the 1 ft. soffit that faces the speakers. I bought some styrofoam/spongey like gutter guards from home depot and layered 3 of them to the top of soffit all the way across, which is 12 ft.  It has improved the SQ. I can hear individual instruments more clearly with more sustain. I'm going to cover the rest of the soffit with these and see what may or may not come about. my guess is the flat surface of the soffit was reflecting frequencies back at the speakers and canceling out those certain frequencies?

I’m not sure exactly what I’m getting at, but a friend used to host a series of live acoustic jams in his good sized apartment. They got fantastic musicians and David Grisman even showed up and played at one. I used to use those events to fine tune my ears (sometimes closing my eyes) to hear what live music from up close in a domestic setting sounded like. The sound and room colorations varied based on my position and players position, just like a stereo would.

The thing that struck me was that no matter the room interaction, the timbre and signature of the live instruments didn’t seem to change even though the room reflections did.