I ended up buying a Neutrik AES/EBU Digital Impedance Transformer Adapter (75 Ohm to 110 Ohm) and their matching 3-Pin Female XLR Connector to which I soldered a 1.5 meter CAT6a cable. The Master speaker is configured to switch inputs via MSR so that both SPDIF and Speakerlink can stay connected, allowing me to more easily enjoy MQA rendering and HAF room correction (using Roon convolution) while maintaining access to other sources through the 568.2mm.

Challenge now is to route these other hi-res digital sources through Roon somehow, like I am able to do from a USB-connected disc player using the CD Entrypoint extension (limited to 16/44).

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