Hey Blair,
I've never worked on a P2K so I cannot offer any solid advice, but AFAIK we should be able to spitball some ideas...
First things first - Have all fuses been out, tested with a DMM, correct value and reinstalled?
Switch matrix's as you know are a nightmare....But keep it simple and from the manual have a look whether its full rows or columns which are out and check the chain to make sure it hasn't been pinched etc...
If that all looks good might be time to remove the big ol' driver board and your trusty DMM....If I was closer I'd certainly swing in as I'd love to get my fingers dirty on one of these!...
