We are currently running the TIMG's hardwired to the Avaya system and then SIP to CUC. However we have looked at, and will be again shortly, looking at going SIP end to end. From my understanding, you need something in between to do SIP header normalization. We have more than likely will be using a CUCM SME cluster to do the normalization. I believe Cisco provides a guide on the setup on their side, don't know if Avaya does on their side.