OK, that’s how I connect from a more recent surround processor in the theater ... but my living room system has only coax out from a 568.2mm (with no SpeakerLink) which sounds very good.
If I run coax to my Left Master and then on via SpeakerLInk to the Right Slave, are there compromises that would make me want to stay with SPDIF?

Server: Audiolinux Roon NUC w/HAF room correction and crosstalk cancellation
Theater: 218, Allo Signature, miniDSP, HD621, C61R, DSP5200SEu, 420, 33, NHT subs
EtherREGEN w/Finisar fiber, Shunyata Denali
Living Room: RPi4 Diretta Host & Target, Ghent USB > Singxer SU-6 > AES NA M-Links > DSP9
Shunyata TritonV3, LHY lps, Farad Super3, Stack AUVA feet