If you have a pair of ASM units, I personally don't see the need to fail open direct to the pool. But I don't have all of the details of your implementation and requirements. What would take both ASM units down? Would you also need to account for a similar possibility of both LTM units going down simultaneously? If you're concerned about the ASM processes themselves, I suppose you could configure a non-ASM VIP on the ASM units and add that as a lower priority pool member on the LTMs.
The XFF logging DLL which Joe created (
Click here) will log the XFF value, but won't change the CGI variable REMOTE_ADDR which IIS sets.
Aaron