it definitely may be something like that.

the toft atb's aux section uses single stereo outputs. the stereo sends and returns are on one cable each. a balanced stereo jack. which i had cables made for.. i'll have to check my send jacks.

but, still, even with a synth plugged directly into the input of the 7600.. with a loud patch.. i get little to no movement on the 7600 input LEDs.