I used to run wires from 4 accordions to a small Behringer mixer, with one send to the house PA. I could set up custom EQ and gain on each accordion channel, but the input cables from 3 single-rows and a triple-row got tangled up pretty good, so I switched to a Boss EQ-20, with signal sent to an ART pre-amp and from there to the house PA. Advantages are one cable in and one cable out to the house, and I could zero out the ART preamp when plugging-unplugging accordions, so no "pop" going to sound system. Boss EQ-20 lets you pre-set and store up to 9 custom EQ settings (10-band), which let me dial in each accordion's optimal sound. Eventually I added a TC Helicon powered personal monitor to the circuit, giving me full control over my monitor settings, and allowing band members to set their own accordion monitor comfort level through the house system without affecting what I heard.