I have enjoyed battery psu with Macs in the past, and have read details about Vinny's dongle for the mR, but thought that is only targeted towards LIO owners. For the best sound from mR, a top quality linear PSU is what to shoot for. I am fortunate that I have a friend who is an accomplished builder who made a custom LPSU for the cost of parts which rival those in very expensive PSUs. So I won't go down the battery road with it.
Yes, you are correct that mR is ethernet input / USB output. I've read about a good ethernet power line adapter kit on the CA site, if you need that. My past has been mostly analog, but everyday I am liking & listening to the digital more and more for first time ever. PM me if I can ever be of assistance. Cheers,
Spencer