OK, I unplugged one of the shaker 500 mini-amps and one of the subs went silent. So, it looks like the regular speakers are driven off the HU, and the amps are only for the subs.

I also tested voltage -- when I did OUT1+ and OUT2- to test for bridging, I saw about half the voltage...weird?

I think I will replace with 2 of these bridged for about 50W into 8 ohms each: http://www.41hz.com/main.aspx?pageID=105

 

Funny... My AIM screen name is Rat Bastard. Anyway... Where are these amps located? In the doors?

 

LOL, my name in my band was Nat Bastard, sort of a joke on Rat Bastard

The amps are by the driver's side footwell, on the left side and up underneath a bit -- easy to find if you stick your head in there.

 

Those TRI-Path amps look like a neat project. What are the physical dimensions of the factory units?

 

Like 2" by 5" or so, tiny. The AMP3 kit from 41hz is like 1" by 3", might leave me room for a LOC or x-over I will probably use passive filters to start since I want to experiment with different settings. The Seas woofers have great midrange response and my mids are cut off at 450hz or so...I think the factory amps do LPF at 250 or thereabouts...