While I hear you regarding the loading resistance, that it should be clear what the setting is, the variable gain is such that, being infinitely variable, you set it for your ideal listening and leave it alone. If we do this, it will be a simple potentiometer, probably with a distinct and limited range, but not with detents.
The only other way to go would be a distinct set of discrete resistor settings with specific attenuation. I just thought that the infinitely variable attenuation would allow for the most flexibility because everyone's system is different. You have preamp gain, amp and speaker sensitivity to consider.
Thanks,
Dan