Is there any architecture doc for empeg?

There's tons of information on this BBS, about every aspect of the player. The problem is that it's sprinkled all over and sometimes hard to find, even with the Search function. There's a project going on to put together a community website which will hopefully become the authoritative resource, but that isn't ready yet.

Here are a couple of links:

sven's site (he says the URL will change when the site is ready)
the developer site (out of date)

If you are interested in anything in particular and can't find it by searching the BBS, just ask. Replies sometimes appear within a few minutes...

Borislav