I would try checking the voltage on the battery itself. it may be on the way out and not able to sustain a suitable voltage. I have the power dip problem but only when I start the car, not for something as mere as using the headlights. I have pop up headlights anyway so I _should_ get more voltage drop at that time anyway. I know you have an internal volt guage meter but how reliable and accurate is it?

Next try running a lead directly between the battery and the empeg always on power. You say it is currently connected to the cig lighter, possibly not the most reliable source. I would run it from the same source you have the power for your amps your amps dont seem to be suffering at this point.

If your lights tend to pulse when playing music at a moderate level it's an indication that your charging/battery systems is on the way to the graveyard.

edit: dang it beaten by tony!