In assembling this combination you will need to update your Jeti RX's to get them into UDI 16 mode. The PowerBox Support Forum indicates this RX update must be Ver. 3.24. That may be true still in Europe where the RSAT 2 RX's are approved for use. In the USA where the 3 channel RX is FCC approved, the correct update on the Jeti Studio site will be Ver.3.25 - UDI 16. Be aware there is a UDI 12 version shown also. You don't want that, it will limit you to 12 channels.

My PowerBox Competition SRS is set up with two 3 channel RX's in Dual Path mode using the Ver. 3.25 - UDI 16 update and works perfectly with my DS-16 TX. You can receive full downlink telemetry by running a Male-to-Male servo extension from the EXT connector on one RX to the TELE input port on the side of the PB Competition SRS opposite the switch lead. Look on the Sensors/Logging screen of the TX to see the PB parameters available, just like you would with a Jeti Central Box. The EXT connector on the other RX is available for another telemetry sensor (e.g., a vario) or multiple sensors through an expander.

More information is available on the PowerBox Support Forum. Look for a message from Richard Deutsch dated July 1, 2015 that discusses connections from Jeti to various SRS PowerBox models. It has the information you will need to configure the RX's properly as well as a connection diagram.