I'm a little confused as to how you would route based on CID. Incoming caller's ID or called number ID?

On all of the fax servers I have done we assigned a DID number to each user as their fax number, ring a virtual extension number (make virtual extension number last 4 or 3 digits of DID Number), forward always virtual extension to Fax Server Hunt Group and make hunt group AA/VM type as well as sli ports in hunt group in order for 7200 to send digits.

At that point the digits will be coming in to the fax server much like a third party voice mail. You may be able to add and/or insert digits within the fax server if necessary for the routing.

Good luck.