you can use a midi cable to connect the midi clock, so they will start at the same time, have the same speed and (if it’s on a volca) you can change the program at the same time.

If you want to, you can send the sound from the volca to the Rytm. Then you can use the compressor of the Rytm (and maybe also the distortion, I am not sure) for the sound of the Volca.