DIY wiring of RCA-to-XLR umbilical cable

[Axel]

Would the mutek add a delay?
Do we know that the protocol between the two units is standard?

I can confirm that the Mutec will add no delay to the signal. In my living room, I have a Sonos Play going into the Mutec, then into my 440 Pro. In the kitchen I have a Sonos Play going into a Creek CAS4040 (30 years old this year and still going strong!). When I group the living room and kitchen, they are in perfect sync.