First, thanks to everyone who responded. Very helpful and got me thinking about stuff I hadn't before. Agreed that speaker placement is important. I found the Song3s to be particularly sensitive in this regard, whether the parameter was distance from back wall or left-right distance, listening distance and height or toe-in. Get it right and the soundstage takes on a nice 3D image with voices and instruments where they should be.
In the aggregate, suggestions were about evenly divided between DAC upgrade and room treatments. I was mildly surprised that neither upgrading the integrated nor improving speaker isolation (e.g., Isoacoustic Gaia 3) was mentioned. Several folks reminded me of the GIGO phenomenon. Systems reveal recording flaws rather than covering them up. First principle, but I dis-remembered it.
Again, thanks to all. Happy listening.