If you’re thinking about conditioning, consider an isolation transformer. Plitron makes a good one - I use four of them - they were among the first to design in North America and build to the highest specification in China. The build quality is German, or better. But they tend to growl while they are doing their job, so a utility room is a good place to site them, certainly not in the music room.
Wall treatment could be Persian rugs, but a cheaper alternative might be strips of wood. I have experienced very good results, both acoustic and aesthetic, from strips of wood affixed vertically to the walls: 1", 2", 3", 2", 1", etc. with 1" or 2" spacing. Some knowledgeable architect specified it for a conversation room at the University library, and one could not hear a private conversation from a few feet away. They used black walnut - well, they would, wouldn’t they?
Another possibility is random lengths 1" to 4" of 2x2’s, 2x4’s or 4x4’s. Cut some (or all) with angled ends, and arrange aesthetically on a plywood backing. Then place the arrangement by trial and error, starting with the point on the wall midway between the 2905 and the listening position.
Different coloured woods could make that very attractive. I’ve seen pictures of that, but never experienced it, so can’t speak from experience. But it should work very well indeed. I’m considering something of the kind for a too-lively kitchen.
Good luck!
