I can’t contribute to the Mixing Link help, but I do admire processing an accordion! Like PRSGUYS13 implied, I don’t see you using the wah & SY ‘in series’ at the same time, but maybe. Or alternately engaged.
Spitballing now (I don’t own any of the hardware mentioned here): Not ideal, but perhaps the send from the SY loop to the wah, then return it to an open mixer channel?
What led me down that path was the wah’s boost capability. You may be able to use it in a mic input, without unbearable distortion.
Just winging some potential options …