Thanks for the summary Tony. You'd cemented in my mind that UPnP isn't universal, is generally a mess, and not worth really investing any time in exploring. I'd come to a similar conclusion after seeing the general state of affairs with clients - there simply don't seem to be any good ones - certainly nothing that comes even close to what I'm already using.

Proprietary is definitely the way to go. I mean, the proprietary system can be open source, but there doesn't seem to be any "standard" that's worth anything at all except as a sticker or check-box on some product literature or packaging.