This was also one of my considerations. I'm hoping to have a decent enough sound without having to go down that road. Might not be possible, but I'll try. I guess, bottom line is looking at the load that the alternator can support, and stay under that. Good thing that my oldest kid is an electrical engineer wannabe. He can do all the math, then we can get back to the real world and see if the calculations work. Hopefully he's still got some contacts at the university because I know they have some pretty heavy duty load resisters to test out the calculations. Only problem there is that I'll need a temporary spare battery until we know the results, because we would be doing the tests on the water under practical conditions. Why waste gas doing tests when you can be wakeboarding/surfing in the mean time?
If we end up going that deep, I'll document the progress.