Then just look at the sources for MXM or for XBMP. Unless you want to learn how to do something specific that only Ava or Unleash has done, then there's no reason why you need those sources. And if there is something specific, just email them and I'm sure you'll get a reply.
Again...if you want to poke around the code of an entire xbox app, then look at the open source apps, and read the development tutorials...don't waste your time hounding the authors of closed source apps. It won't get you very far.