Many thanks for your input. It seems like 7.1 probably is worth it.

Looks like we have settled in with a media lounge size of 9x7, which would be shared with the Grand Piano.

Lounge: 861v8 with ID41, 218, UHD722, Sonos Connect Wyred4Sound, AppleTV, Oppo 105, DSP8000SE, DSP5200SE
Streaming: Roon/Spotify
Currently not in use: DSP5200 x 2 pairs, DSP5200HC, DSP3200, 218 x 2, MS600, DSW x 2, MC200, Sonos Connect Wyred4Sound