It is very important to me to keep left and right channels symmetrical and with signal wires as short as possible. For this reason both the input selector switch and volume control need to be centrally aligned, this solving both requirements. The only way I can get this to happen is to reduce the size of their knobs to 15mm diameter. I don’t think this looks quite as good as the previous layout with larger controls and the volume control being the largest, but it is still acceptable. I have tried using this size of knob and there is enough torque to turn the controls so no problem there.
This is what the current layout looks like. I have added a gradient outside the input and controls (but not the headphone switch) as these will be recessed so that the edge of the them that is closest to the inside of the amp is set deep into the cabinet. I’m not sure how clear that is in the drawing, it’s as close as I can get it for now.