I didn't get any response and later the sales team confirmed it was not supported. As this was a while ago, things might be bit different now.
It is not applicable for us as we ended up going with ACME SBC which supported SIPREC.
From the debugs it seems that SIP notify is getting negotiated and DTMF is being sent across.Try putting a number expansion to hairpin the call out again to PSTN. Send the call to an IVR with menu option. For test purpose call Cisco TAC Toll free num...