A Crossover Pedal is needed. I have stereo pedals and 2 combo amps. Put a crossover in a box, have 2 inputs, 2 out puts. A mono/stereo/crossover switch. Crossover frequency control. Take any pedal that doesn’t have a stereo version and add 2 of those into the box. The EHX Analogizer or Comb filters. Make it good for acoustic, electric, keyboard or ukulele!