fwiw, to answer my own question...
I actually use a laptop as my server, so it can sit on the shelf, with the lid closed, and remain mostly out of the way. I keep a mirrored pair of drives attached via USB -- I had first tried an eSATA card -- that was fast, but would periodically dismount a drive, so I reverted back to USB.
I keep all my data on the external drives, and I share that directory over my LAN. I also keep a printer attached to this 'server' laptop.
So, I back up all my PCs to the 'server' -- which winds up mirrored onto two drives, and I also maintain a copy of the media files this way.
The 'server' is also connected to my stereo via USB (the receiver, an Outlaw Audio RR2150 --
Outlaw Audio -- has a built-in USB DAC).
So, I can use Remote Desktop to control what happens on the server from other PCs on my LAN, and I can the use other PCs to play MP3s/FLACs/Rhapsody/Pandora/Internet Radio on the server, which then passes into the stereo.
I also use my software (which uses PHP) to present my collection as a site that I can browse and play over the LAN -- so, for example, if I'm working in another room and I want local playback, I can call up the site from the server, and have the music play locally (ie, as opposed to using Remote Desktop to control the server).
I should also add -- I find Apple software to generally be a pita, and so I tend to avoid it...