It seems you would have to create a psuedo-database that contained all the playlists of the various empegs on the network into one database,

Yes, you'd have to create a database. Nothing pseudo about it!

and replace the player database with your new one.

Oooh, only if the web app itself were running on an empeg. I'd recommend you did it on a full-size PC instead; the database agglomeration stuff will probably need lots of memory and CPU. Or, at least, lots more than an empeg has.

Then you'd just need a way to mount a drive over the network.

No, you could just stream off the empegs using those parts of the existing protocol that Jemplode's backup features use.

And when you've done it, make it serve Rio Receivers!

Peter