Software to stream music on demand

The only thing that springs to mind immediately is VLC, which I know supports a slew of streaming functions. Whether it can do on-demand streaming of random files, though, I do not know.

I know CenterStage and BackStage have that functionality, but you'd need to be running 2 Macs, which probably isn't much help in your case.

I'd look up "media backend servers" or something to that effect on Google. You might find something to build an iTunes-esque database of your music files and then a companion frontend to stream them, or even better, a backend that works with standard protocols.

Jam it back in, in the dark.