racheskiThey've been using the same design for a while. I guess either not enough people cared about it, requires compromise in terms of engineering, or they just don't want to change it.
racheskiThe gain switches just reposition the volume control so that you have a wide range of adjustment. The main purpose is to set the best gain for your source not to adjust gain for different headphones.
HirakYou can look at it from either side but you're achieving the same thing. Since some headphones are more efficient than others and some DAC's have a higher output, you're trying to adjust the volume control so that you have sufficient gain and yet not too much gain. The goal is to have the volume control roughly around 12:00 when listening at a comfortable level.