Hello, I use this also for the expression pedal to be able to control my X1 & SD1 ( I EQ for separate), I made this work also when I had the VA7, to be able to work properly, it needs to share the same "ground", and for matters of polarity, I use a short simple stereo RCA cable w/adaptor stereo to plug 1/4 in each end, one to the my splitter "Y" the other to the keyboard, and if it does not work( the sustain/volume of the kb), simply invert ONE of the ends of the RCA cable.......

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mdorantes