As far as I know, the empeg guys are still debating what to do with the "hold down the volume knob" action, and one of the ideas presented was that this should switch the source. Dunno if that's what it's going to end up being, though.

As was already stated elsewhere in this thread, you can use Mark Lord's Hijack kernel to do exactly this if you like. It's what I do, and it works really well. (As I recall, wasn't I the one who suggested that to Mark?)