You will need some kind of gateway to do this. The reason is the SX20 (and other hardware endpoints) uses H.264 AVC, and Microsoft uses H.264 SVC. They are not compatible, hence the need for a gateway. Before 2016 the Cisco solution would have been a Lync/Skype (functionally the same in this conversation) gateway, which would have been a VCS/Expressway with a license key on it. Since the Acano acquisition early last year, the best solution now is the former Acano product, now called Cisco Meeting Server.
http://www.cisco.com/c/dam/en/us/td/docs/conferencing/ciscoMeetingServer/Deployment_Guide/Version-2-1/Cisco-Meeting-Server-2-1-Single-Combined-Server-Deployment.pdf
