Speed Sensor for Axiom Pro

I am upgrading an E120 classic system to Axiom Pro. The current system has a DSM-300 Module with the ST-800 Speed/Temp Sensor combined with a B260 Depth Transducer via a "Y" cable. The DSM-300 connects to the E120 via the SeaTalk HS switch.

I want to upgrade the dual frequency B260 transducer to a CHIRP capable B265 which I understand connects directly to the Axiom PRO RVX unit.

How do I add the ST-800 (or some other Speed Sensor) to the Axiom Pro System.

Thanks,

Jon Spain