Thanks for all the suggestions!
A big problem with this system is that the listening area features A LOT of glass, a design feature to showcase wonderful mountain views that cannot be compromised. Additionally, ceiling height in the listening area is only 7 1/2 feet, which is not helpful.
I'm thinking a demo (loaner) line stage is a reasonable path to testing the potential benefits.
Also may order a few portable acoustic panels from GIK Acoustics (relatively inexpensive) and see how much I can improve the room (and hide them under a bed when not in use).
A ceiling diffuser would be ideal, but a no go with the missus so ...