[quote author="tdstotler"]The possiblity of getting 2 more
channels out of it sounds quite interesting.
[/quote]
I don't think it looks that difficult. The only bugger is that most of the PCB holes have been soldered closed, but these wouldn't be difficult to de-solder, and you'd have to drill some chassis / front plate holes.
There's no hard wiring as such, so if someone can list components and values then you should be on your way.
And for reference, you have two channels to compare to!
Having said that, I'd maybe want to leave it alone and build something from scratch.