Have you seen the Audiotron? It's a bit limiting for MP3 collections as large as yours but it's workable and it's a standalone unit. Basically it fits into your stereo rack, you run a CAT 5 cable back to your hub and the Audiotron will read all the data off of the shares it has access to on your network and stream music over the network through your stereo. I have one and I like it. My MP3 collection is comparable to yours in size and it is manageable, especially through the web browser interface.

As a side bonus, it also plays Internet radio.

Here is a link to the Audiotron on Turtlebeach's page.

Sounds like the new Rio stuff is probably more robust than the Audiotron but given the size of your collection, this might be worth looking into.