FYI, solved this over in a facebook group.
https://www.facebook.com/groups/hxstompofficial/permalink/352242185655984/
Need to split with path A all the way left and path B all the way right. Put the cab in one of the two paths after the split. On merge, also pan path A all the way left and path B all the way right. I added an echo to the cab path to get obvious audible proof that the two were completely isolated left/right. The merge block:
The split block:
I'm not sure why the split block matters as the path in mono to that point. I think all this does is to only send the left along A and the right along B but this should not matter. And, even if the signal was stereo, I would want to mono mix of both left and right sent on both A and B paths. Maybe someone smarter than me will chime in...
