Okay, I think I am almost there - I had the Centre on the slave side which was the problem. All the fronts are working, but the SW no longer works. I have it set to channel 2 and it is plugged in to SL2 next to the centre on the slave side.

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