Hope this helps, I'm not familar with Ikon Fax Server.
I set up a much simpler version of this with one DID number. I created a hunt group with four analog extensions. The four extensions were wired to a Brooktrout fax board. I built an incoming call route for the DID and pointed it to the fax hunt group.
If you did the same thing but just created an incoming call route for each DID (you may not have to create all 100 routes depending on your DID scheme) I think this would work. I believe the incoming DID number is passed along to the fax server. It would be very easy to test with one hunt group and two DIDs.
If this doesn't work, another option would be to get a PRI CSU/DSU. It should be able to route calls to the IP Office or the fax server based on the incoming DID. You could call Adtran pre-sales support (800-615-1176) and they'll tell you exactly what you need to order. I'm sure Kentrox and Paradyne, etc make something too, I've just had really good experiences with the Adtran pre-sales people.