Sorry, but I know this individual well and he is as knowledgeable as anyone around here.. He was trying to be instructive. Changing the gain with a set of different value resistors - by definition, has nothing to do with the "quality" of the sound. Perhaps he should've elaborated, but as I said earlier, the point was well made, IMHO.
Want to change the "sound quality" of an amp? Then suggest changing the sound-affecting components - capacitors in the signal path, opamps, buffers, transistors (in zero-feedback topologies), etc. However, changing gain does nothing but change the relative position of the volume knob in relation to the output volume.
Yes, there are instances where the gain may be jacked up enough that it's easy to tell that there's some residual noise or hiss in the output. However, that is never going to change the sound signature of the amp.
Maybe that explanation helps?