This is what happened when I watched a rig rundown by Royalblood's bassist...

Bass amp (1x15 Roland Spirit 50w) gets the clean signal from the bass
Guitar amp (2x12 Lab Series 100w) gets the output from the GT-6B. The GT-6B is cranked up with a fuzzface sim and the synth sim (with frequency controlled by the exp pedal).
Immense sound...! Though I'm sure I can find a more suitable amp than the lab series. It's rather heavy and doesn't seem to like the bass or GT-6B.

Bass amp (1x15 Roland Spirit 50w) gets the clean signal from the bass
Guitar amp (2x12 Lab Series 100w) gets the output from the GT-6B. The GT-6B is cranked up with a fuzzface sim and the synth sim (with frequency controlled by the exp pedal).
Immense sound...! Though I'm sure I can find a more suitable amp than the lab series. It's rather heavy and doesn't seem to like the bass or GT-6B.