You might check out JRiver Media Center. It's not free, but it's only about 50$, and it supports all sorts of streaming and remote control.
For instance, I have it running on my file server, audio out is connected to an amp, which then feeds some outdoor speakers.
MC has a built in skinnable web server that can.
1) stream audio to a web device for playback over that device.
2) allow a web device (in my case a windows phone 7 phone), to remotely control what's playing at the server, so I can use my phone to control what playlists play, or select individual tracks out by my pool. Anything that can browse the web can do that.
They also have some dedicated mobile apps (specifically for iPhone, but I believe it works with Android, not WP7 yet), that work a little smoother than the web app, but it works quite well for what I do.
Couple that with a remote streaming device (like a roku maybe)( and you can easily get access to all your music on your main HT.
Plus, if you want, MC also has a "theater view" that's specifically designed for running on a box that controls your home theater, you can select movies, audio, internet radio, record, blah blah blah on the HTPC you install it on.
Supports plain old remote controls, too, which is pretty cool for HTPC applications.