What have I done? Finally got my Sonos Connect plumbed in via optical cable to the Pioneer amp in the dining room - the combined sub/amp I got to satisfy Mrs. Scene's desire to have a more discreet system - set it to pure direct and ran some test tracks through it.
Then I put the main living room system in synch with it and walked back and forth between rooms to see if what I was hearing was true. Then I asked Mrs. Scene what she thought... And we agreed, the cheap and cheerful, cobbled together system in the dining room sounds better than the Arcam + Monitor Audios in the living room. Even when I put that on stereo direct as well.
I may have to lie down for a bit...