Cool, I have a few options to try now. I have installed WinAmp and it seems to be working, though it is a different solution than I was originally looking for.
I was originally thinking of a 'thin' client that would just talk to my UPnP server (like the PS3 does) and take advantage of all the cached info there. Winamp worked by making it's own local cache of my shared network folder (took an hour or so), but not by being a client to my pre-existing UPnP server.
I'd still be interested if anybody knows of a true 'thin' client solution. However I am rolling with Winamp so far.
