Pro-800 Midi Thru Question

I've just made a little synth setup, after a few years out of the synth game, trying to get some budget Alan Horwarth horror soundtrack vibes (it is the season, after all).

Basically I'm going my old Roland A800 MIDI Controller -> Pro 800 -> ProVS, because you can easily change the MIDI channel on the A800. So I set up the Pro 800 on channel 2, and ProVS on Channel 3. I tested this (A800 direct to Pro 800, only works on Channel 2, and A800 direct to ProVS, only works on Channel 3) and therefore thought that if connected in the above chain (A800 -> Pro 800 -> ProVS) I would be good. But unfortunately the ProVS doesn't get triggered by the A800, when I switch it to Channel 3. Am I missing something in the MIDI thru setup of the Pro 800, or is there something in the ProVS MIDI setup that needs tweaked? Thanks!