I believe both the RJ and RPM splitters use the "standard" of DMX on RJ45 pins 1 and 2, expecting standard AT&T T568B wiring (to get the twisted pair on Cat5), with DataA on Pin 1 and DataB on Pin 2.
I can't confirm that, though, because DIYC is now down for the fourth consecutive day ...
Keen on this idea as I said. I used two splitters this year with one in the garage out of the laptop with output to my wireless transmitter and then out to the yard with the other two. Getting away from the 230v transformer is a great option!
I am going out to the rear of the section next year so another couple would be handy.