Cisco has released a new version of the MCU software solving one of the caveats with using SIP on it. Finally the separate content channel will be available in encrypted sip calls.
There are other fixes such as added support for Clearpatth and automatic disconnection of inactive calls (finally kills those pesky jabber.com clients ;)).
There are lots of other improvements so please read the release notes properly.
You can download the software from Cisco here