Sounds exactly like a job for mpd. For control, use any of Sonata (python/gtk+ client), mmpc(?C?/gtk+ client), or mpc (scriptable CLI client), all natively, or some others via Debian chroot. As the existing clients have a playback-control emphasis (suited to the N810 end), it might be worth coming up with a display-only client for "normal" use on the N800, and start one of the aforementioned ones when local playback control is desired.