what is the largest gig slave drive I can add to my mk2?

If you are planning on buying a warrantied drive from Empeg, then whatever they've got up at the Empeg Store is the largest you can get.

If you are willing to void your warranty, then it can can be pretty much any 2.5" laptop drive you can get your hands on. Whatever the biggest one is. See the FAQ section of the BBS on the exact specifications for the disk drive.

___________
Tony Fabris