Here is a blurb from an email they sent me:

The JrX System is a simple radio trigger (does not support iTTL or High Speed Sync), compatible with just about any light out there. The JrX Transmitter features a hot shoe attachment with a contact pin, as well as a 3.5mm sync port to connect via PC sync of the camera body. The JrX Studio Receiver has a 3.5mm sync port, as well as an RJ-11 data port for Paul C. Buff strobes (which it supports remote power control from the group dials of the transmitter). When paired with the JrX Studio Receiver, the RPCube enables remote power control of the Canon or Nikon flash in analog TTL mode. The RPCube is simply telling the flash to trigger at full power, but it quenches it according to where the corresponding group dial is set on the JrX Transmitter. Unfortunately the SB-910, SB-900, and SB-700 do not have an analog TTL mode, so you will only be able to trigger them in manual mode (which will need to be set on the flash itself).

Since the PX and JrX operate on the same radio frequency, you can also use the PX Transmitter to trigger/control the JrX Studio Receiver. The PX Transmitter has the group dials of the JrX Transmitter built-in to the menu, so you can use the P and X buttons to control the power output of compatible lights.