Right on! Totally solved this problem by watching a Cuckoo video. Big thanks @cuckoomusic !

The issue I wanted to resolve was how to make other synths louder on the AR input. OP-1 was super quiet, korg volcas super quiet. Solution: OP-1 drive knob. I just plug the OP-1 in and crank the drive and it gets loud as heck without sounding like barf. Granted it does compress the heck out of everything coming out of the OP1, but as long as I’m not playing multiple tracks with many instruments it works just fine. Ok so what about the volcas ? Easy plug the volca into the line in of the OP-1 and turn up gain in the input settings and boom loud volcas+loud OP1 with Analog RYTM.

Can’t believe the solution was right in front of my face the whole time and I didn’t need to buy a single other piece of gear. I thought it was an issue with the type of output from these battery operated 1/8" stereo jack type devices use.

The only thing to tackle next is - how the heck do I get the OP-1 to be less noisey when USB is plugged in. LOL