I'm about half way through developing my whole-house audio solution, but I just use the tablet (N800) as the remote control interface for it since using a small embedded PC was much more cost effective than another N800 when I started the project (even today the catch with the N800 is that the audio out is not great... it sounds okay, but if you hook it up to some decent speakers, it's just not that great in comparison to the average mid-range PC soundcard). The fact that the N800 can't double as wifi access point was also a sticking point.

Anyways, I'm not sure how far/in depth you're planning to go with it, but if you're looking to do more than just a single room setup, I would recommend looking into something more along the lines of having a single N800/machine/device somewhere that will hold your media and handle playback, and use something like PulseAudio to distribute it/share it to other devices. There was some talk a while ago of porting Pulse over to the N8x0's, and I understand that it's going to be included in the next OS anyways, so it depends on your timelines for the project. The main advantages to this approach are that you can then share synchronized playback across multiple areas/rooms, and you only need to have one location for all of your media.

If you're looking from a multi-tablet point of view you can theoretically do the one location for your media by sharing the USB drive/whatever over the wifi network but I think you'll find performance problems if you try to access it from more than just two or three devices at a time; also, no way to do proper synchronized playback (i.e. two N800's in two rooms beside each other both playing the same music in sync with each other). MPD is a much better road for this than VNC as VNC performance really is quite poor from a general "end user wants to be able to use the device without problems/lag/delays/etc".

Good luck though, look forward to hearing about it!

Thanks,
-Rob