Success! Volumio streaming over wifi via UPnP/DLNA from Minimserver on a Windows 10 machine, controlled by either Hi-Fi Cast or 2Player on an Android phone. Previous solution, WDTV Live Plus, worked well but I feel like the RPi & Digi+ (not Pro and without the output transformer; went cheap as I'm connecting with Toslink) is giving more detail into the Mimby*. The WD unit might suffer from not great optical implementation (see Archimago). I chose Volumio over Rune despite the caveats above only because I read somewhere it was small enough to fit on a 2Gig card I had lying around. It didn't, but I'd already downloaded it, so... One odd thing is that it seems to need its wireless hotspot enabled as well as connection to my local network to play more than one track at a time. Not sure why this should be, need to look into it further. Echoing many others, thanks @Kattefjaes for the encouraging documentation. *for which, thanks again @msommers !