distortion between Ableton and Korg FX Pad

Hello,

I'm having a distortion issue that involves sending audio from channels in Ableton through a send (ext. out to Korg FX pad) and back into another Ableton channel. I'm using a Presonus Firepod to route audio from Ableton into the L and R inputs on the back of the Korg and I'm using a mono cable from the Korg out to one of the Firepod's inputs.

The sound from the audio channels going to the master is fine. But when the send on said audio channel is turnes up and passes through the Korg, the returning audio is distorted. The distortion isn't very loud, but it's particularly annoying at higher volumes and is amplified a lot if the HP or LP filter on my source audio channel has the resonance cranked...this is very unfortunate, cause I like to like to have my res boosted

I've tried switching out the cables between the Firepod and the Korg but that didn't help. So either the Korg is faulty, the Firepod is faulty, or I've somehow overlooked an issue with my levels in the software. Any suggestions?