From that same Tonehammer thread back on Talkbass, I understood the AGS switch on the pedal to essentially be similar to having the drive knob at minimum or maximum. E.g. you can crank the drive and still have no drive if the gain is low - increasing the drive kind of lowers the headroom so that the gain knob causes more distortion, as well as gradually bringing in various EQ shifts.
So you can get different mild overdrive sounds - drive set high and gain set low, or drive set low and gain set high, or anywhere in-between.