In addition to the PX2 power supply and a stereo cable, you will need the DI box that usually comes with the basses. If you are unable to find one, you can build one yourself. It's just a DC power supply and a direct box in one chassis.
The Ethercon connector is for connection to a PODxt Live/POD X3, or whatever the latest POD is with a Variax input. (Or the Vetta amps, if I recall.) That won't be of any use to you if you intend to use the 1/4" output. They never developed the Variax editor software for the basses, and nor did they implement pitch shift options. Note that in any case, you should NOT be using an RJ45 cable for the digital connection. It is very easy to damage the jack that way, which is why the Ethercon connector was chosen, with its protective shell around the RJ45 connector in the center.