HPF @ 3.7Hz worst case (all Aux1-4 dialed in full CW and all assigned pre- or post-EQ, external Rin assumed 10K) doesn't look that bad. Double up C15 (pre-EQ out) and C25 (post-EQ-out) to 100uF to get this HPF an octave down if it helps better sleep. How well the TL072 (IC2 and IC4) behaves is another subject, when driving this worst case ~900 ohms load (R21,R24,R49,R50,R51R52,VR8,VR9,VR10,VR11 + the assumed 10K external load all in parallel).
I wouldn't call the connection of Con1-pin8 (insert send) to another jack or multipin connector a mod, but YMMV.