Hi Jon,
I was using that same camera (literally - you waiting for my camera to arrive tomorrow!) on an ED80 with a field flattener that had 55mm of back focus.
I had it set up like this without issue:
scope > field flattener> spacer > filter wheel > camera
With your original setup you may experience vignetting by have the sensor so far from the filter wheel assuming you are using 1.25" filters.
Dave