Virtual SoundCheck MADI Issue

Hey!

I’m sending signal from my C3500 with a MADI card to a MADI interface into my iMac.

Using REAPER, I’ve got all the signals successfully coming in to the right spots when I enable ‘record send’ under virtual soundcheck on my surface.
Vox 1 goes to input 1, vox 2, input 2, etc. All is well!

The issue comes when I try to do virtual soundcheck.
Using totalmix FX, I’ve got software playback channels 1 through 6 routed respectively to hardware outputs 1-6.

Vox 1, when playing audio back in reaper, works great. In virtual soundcheck mode, the audio plays back as if it was Vox 1 on my surface.
Vox 2, the same.

Now, when I get to other channels (lets say Vox 4), I notice that the audio from REAPER in that channel is coming through channel 4 on my surface (good!) but it’s ALSO coming through channel 36, or other channels seemingly at random.

Why am I getting duplicate audio? Am I missing some sort of audio routing linking or something like that?

Thanks,
Joanthan