I think the issue is not whether to have a balance control or not. the issue is that it's nearly impossible to adjust the volume without affecting the balance. As you know, the channel balance is very important and it's changed every time you adjust the volume.
Look at Stax amps. They have balance control, but you have to make an effort to adjust it.
For the Koss amp, I either tape the two knobs together or I also have a white line on both knobs so at least I can visually line up the white lines to know that I am at equal output levels.
True enough -- one of the issues was the ergonomics of this particular concentric dual pot. The comment I was objecting to was whether a balance control has any use in a headphone rig. This is a seperate issue. I am also not sure how accurately the 2 sections of the pot track each other, especially at the bottom end of their range, so I would "dot" the controls by ear, or by measuring output with a calibration signal...