Voltage is easy enough to measure with a multimeter, so you shouldn't have a problem checking various wires or right at the battery terminal for a dip.

If your wiring isn't at fault, and you are just sucking too much power from your charging system, then you should be able to run those 2 15's with a more efficient amplifier as suggested. Of course, if you didn't mind spending money, you'd replace those 15's as well with something smaller, which will be tighter and _can_ be just as loud.

I have found that one SONY adapter is model XA-107 - don't know if it will be the one for your head unit. Then there's also the XZ-300 which sounds pretty damn cool but is definitely overkill (it allows multiple RCA aux sources into Sony's unilink). It's available at Crutchfield.

Just search google.com for "sony aux adapter" and search the funmp3player forum I told you about for "sony aux" or "sony adapter"

Bruno