I was reading the GPX5000 manual and from what i have read, it seems to automatically know that you have plug in a external speaker. I can only presume that it senses the ohm's resistance of the speaker. I think that most booster speakers run at 8 ohm, is this correct? Have i interpreted the manual correctly? I would believe that if you were using a 8 ohm external speaker that you would be using more battery power as the internal booster would come in.?