Alex, actually the "gain" isn't what's being adjusted by these settings. Audio amplifiers have a fixed gain, typically in the 25-30dB range. This gain is often set 6dB lower on a balanced XLR input to compensate for the double voltage that's coming in on that input(a doubling of voltage is a 6dB increase)so that the volume is the same on either input at a given level setting. The level controls on the receiver/processor and sub are variable resistors which adjust the amount of voltage being let out/let in to be subjected to the fixed gain of the amplifier.
