the voltage is actually 14.8V with the engine running. Which should be enough for anyone...

Yeah, but how big is the battery and alternator for that little 2-cyl engine? I mean, its charging system was designed to fire two spark plugs and *maybe* some dim headlights once in a while.

Here's a question: Are you connecting the amplifiers and the player's yellow wire directly to the battery (through a proper fuse block of course), or are you tapping off of one of the factory wires? Maybe the battery supports that kind of current draw, but the factory wiring does not.