Daniel, Jason's reply is right on as far as the setting on that control goes. Incidentally, it isn't a "gain" control; audio amplifiers have a fixed gain, typically in the 25-30dB area, which boosts the incoming voltage around 30 times. That level control is a variable resistor which can let in almost 100% of the incoming voltage to be amplified or let in almost none.
How quickly the control "opens up" can be varied widely and doesn't have anything to do with the maximum power available. My EP500 has the older control which used a typical setting about 1/4th of the way up, but this certainly doesn't mean that it has more power than yours which uses about a half way setting.
