Roland Drum Splitter issue

I have a Roland TD-9 and a few weeks ago I'd bought a fourth PD-85 tom pad which was added to the Aux input. FYI I had previously expanded the kit with a second crash in the Crash 2 input.

I also wanted another cymbal and I'd read about splitting the signal from one of the toms (as I don't use the rim sounds) to do this so I bought this splitter from Amazon (a Roland one so should work right?!) and a 9-inch Lemon Splash in the Black Friday Sale.

I have put the single end of the cable in the Aux In and then the other ends I've put in the 4th tom and into the new splash. The Tom head pad triggers the tom sound on the module but nothing happens when I hit the cymbal (aka the rim of the Aux input). I reversed the lead from tom to cymbal and vice versa, and the cymbal then triggers the tom sound but the tom then triggers nothing.

So the cymbal and tom units work as triggers but the Aux In rim trigger doesn't seem to trigger anything. Is there a setting on the module I need to change to make this work? Or does it seem like the cable is not working fully?