So I have refigured out the speaker wiring. I will be using previously recommended Metra adaptor to connect my head unit. The only audio signal going through the adaptor will be the 5 volt signal from the front left and right RCA cables from the headunit. (White and Grey). The other two supplied RCA cables (purple and grey) are clipped off near the adaptor. This low level signal which will be separated by the previously mentioned "4 channel amp mod". This will be the signal going to the front door panel speakers. I plan on installing some 300 hz bass blockers in the wiring going to the door speakers. I will probably put the blockers in the doors and install some sound damper material at the same time. So the performance of the front speakers should be the same as "the cheapest sound fix".

The rear right and left rear output will be some wires from the other connector on the rear of the head unit (rear right [purple/ purple black] and rear left [green / green black] ) connected through long wires to the exciters (speakers) mounted on the back panel below the roll bar hoops. These back panel speakers have a bass blocker (capacitor) that keeps frequencies less than 300 hz from going to the exciters. The inline blockers are held down by Velcro in the cavity under the rollover hoops. The amp in the head unit will drive these exciters directly. I think it is 15-20 watts which should be plenty for the exciters.

So in this configuration, the preamp on the radio will have an equalizer and fader for these two sets of front and back speakers that can be adjusted. The equalizer setting is for both set of speakers, so I can't have one "equalizer curve" for the front and another for the back, but I will have balance and fade

I replaced the subwoofers in back with forward facing Kicker 2 ohm dual voice coil units. The are connected with the stock wiring back to the original Infinity amp that has been modified to be a four channel amp. The inputs to the stock amp are some RCA cables plugged into the left and right subwoofer outputs of this head unit. This head unit has separate subwoofer controls for frequency and loudness adjustment. The sound output from the 5 volt RCA cable setup combined with the modifed original amp and forward facing woofers. should be pretty good.

I should be able to retain the speed sensitive volume levels with this setup

So I just have to finish the wiring and test connect it before buttoning everything down.....