There's a bigger issue at fault here I think. I run stock discs with very aggressive Performance Friction carbon pads, and after a few trackdays there's not a mark on them (although they do have a nice lip now, hence me fitting a set of matching PF discs next week). Given that he's using far better discs with equivalent pads (not entirely sure on the heat range of the 2500s, but would imagine they're broadly similar to my PF ones) there should be no cracking like that at all.
What brake fluid are you running? When was it last changed? When you say you do a cool down lap, I assume it's at a speed where you don't have to touch the brakes at all? If the bedding in procedure for the discs (note: Not the pads!) has been followed correctly, then nothing like this should occur. Possibly faulty discs? Be worth contacting DBA regarding this and seeing what they say.