i think the mk2 has a new upgraded feature from the ttx. iirc, i did see they offered the mk2 to previous years (06/07). i think i seen it was 1500.00 when i was searching for my rear shock. where exactly i found it, i dont remember. sorry
I know they are changing the casing from aluminum to steel to avoid excessive flex. They have also upgraded some internals such as check springs on the back of the main piston. The check springs are available now, but the casing is hard to come by at the current moment.
BTW....the TTX need revalved anyways to work well IMO.