So far, to save rows and CPU, I send my gtr to my stage amp via FX Send 1 (the block is on the last row just before the amp capture / cab).
Please code Loop blocks to Send 1 & 2 + Output 3 & 4.
Have also the volume knob to be active on these blocks.
Saves rows, then we can use the volume knob to control output. (so far, volume knob not assignable to Send blocks)