Thank T. That is exactly what I was trying to say. For a full range speaker the bottom end will distort while the high end is piercing with a ton of power. Now PA speaks have certain range that they are built for and can handle that much power. Plus most of the time they are parallel with one another on the same channel of said amp. A single coax full range just cant operate efficiently (good SQ) with too much power. I hope that made sense.

 

From what few Rushmore systems I have heard at dealerships that makes sense. They tend to sound clean with decent bass in the dealership. I suspect that is because they are not being over driven to get loud.

 

I picked up a arc 600.4 locally for a decent price. I was going to set the gains with my multi meter at the low end of the recomend RMS watts of the speakers and mark it where it exceeds that.
After I get a basic setup done I will have the local shop that builds Sql cars look at it on an oscilloscope.
I also found a nice RCA cable that others might like for running a 4 channel amp from a single line leveler