As detailed by Bruce elsewhere on the forum, I added MQA full functionality to our system with a Cat 6 ethernet AB switch.

SpeakerLink outputs from our 861 and (in my case) 818 into the switch, common output line from the switch to our Master front speaker (with the other front speaker daisy chained off the Master). Both 861 and 818 programmed as Controller.

Position the switch to "A" and I run 5.1 out of the 861; switch to "B" and I run 2-channel (full MQA capable) our of the 818. It works well, albeit a bit clunky. (Using a remote controllable switch with Crestron or equivalent would be smoother.)

I did worry about SQ of the 218 versus 818, so applied a windfall that fell into my lap to the higher quality source.

John

Main: 861v8, 818v3, 8000XE, 7200HCUSE, 7200.2, Roon Nucleus+, Shunyata Everest w/ Sigma XC and Alpha NR's, HD621, Oppo 103D, Panasonic P60ZT60 plasma. RJ45 switch on master SpeakerLink lines to select 861 or 818, Etherregen & ENO AG feeding the 818, M-Links.
Room #2: 5200.2s from M218.