Thread resurrection, my apologies. FWIW I had much more luck using a midi channel/loop controller (Decibel Eleven Switch Doctor) and a passive volume box to drop the volume of channel 2, instead of trying to boost the channel 1 volume. Very little attenuation needed to even out the levels, next to no tone loss. Every time I boosted the channel 1 volume (keely clean boost, etc) it added a lot of hiss.
Just a PSA as this is a rad amp, but drove me nuts. I found this to be an excellent work-around. Now if I could only gain out ch2 and clean up ch1 without adjustments.