I think to translate addresses from the DMZ to Addresses on the the inside interface of the second PIX, I would suggest perform ing nat translation at the nat router with" ip nat source command" which will translate "source address(DMZ inside interface adress) to an address of the outside interface(i.e, an address similar to address range of PIX2 nside interface).
Contact me back if u r not able to understand my suggestion or need any clarification.