well, they have the delay ‘grit’ knob in there and the pre filter ovd knob is in the amp page - some things don’t fit in the UI or tie up with the diagram, just laid out that way as a compromise, but the SYM indeed works on external - there’s more on this in another thread … !
perhaps the magic happens here
Edit: Or just after ? according to this thread …
http://www.elektronauts.com/t/dist-sym-control-noise-floor-panning/8520/78496