I appreciate this message refers to a very old post, but I have EXACTLY the same problem and would love to know if you got this fixed in the end and how ?

Basically Cisco gateway not sending DTMF events to the ISDN when they are received by RFC2833 however do get sent when received by SIP INFO.

[original post]
http://lists.freeswitch.org/pipermail/freeswitch-users/2009-December/050780.html

Thanks
Bernie