Hi, Thank-you for any input or suggestions:
I have purchased a 1996 Ford 15 passenger long Van which I am changing into a 11 pass "fun party/camping trips" van.
At appropriate times I want to be able to throw open the side double barn doors and other doors and blast the music from the 6- 6x8 speakers and 2- 8" subwoofers.

I'm a shade tree mechanic and have installed a good number of after market stereos but rarely anything with a separate amp.
I'm a bit over my head and this stuff can get confusing for me.

So some questions come to my mind that I haven't found any answers to yet for my van set-up.
Also I need outside recommendations to help so I can move forward with complete success.

THE VAN:

The van had 6 worn out factory 6x8 speakers(Factory placements: Pass & Driver's door, mid van driver's wall, larger barn side door, rear driver & pass door).
I've replaced all 6 with Pioneer 6x8 TS-A6886R, Specs: (350 Watts Max Power (60 Watts Nominal) 4-way, 4 ohms impedance Frequency Response: 34-34,000 Hz Sensitivity: 88dB).

The van already has what seems a good, older(2009?) Pioneer head unit DEH-P3100UB
Specs: (MOSFET 50W x 4, Two-Way Crossover with separate High and Low Pass settings, 2 pair (RCA outputs: Front/Rear or Front/Sub).
It has a CD player I'll probably never use and does not support bluetooth to phone for music connectivity... but does support IPhone data charge cable for music, and I have an iPhone.
Seems I should keep this head unit till it goes out, it may prove more reliable than newer ones..

I have purchased for install:
SubWoofers: 2-Pioneer 8", TS-SW2002D2
Specs: (600 W Max (150 W Nominal), Sensitivity: 86 dB, Recommended Enclosure: 0.15 - 0.50 cu. ft. or Free Air, Dual 2 Ohms, 20 Hz to 200 Hz).
I bought these because the seem to be the largest that will fit, one above the other, in the cavity of the smaller of the two swing out barn-style side doors of the Van, without much modification.
I hope these aren't disappointing, I see some people say SubWoofers should never be under 10" min...

Amp: 1-Pioneer 5 channel high power, GM-D9605
Specs: Class FD, Max Power 2,000 Watts:
Max power @ 2 ohms: 200W x 4 (A/B), 1200W (SUB), Nominal power-RMS @ 2 ohms: 100W x4 (A/B), 600W (SUB)
Max power @ 4 ohms: 150W x 4 (A/B), 700W (SUB), Nominal power-RMS @ 4 ohms: 75W x 4 (A/B), 350W (SUB)
Frequence Response: A/B CH: 10Hz ~ 50kHz (+0dB, -3dB) / SUB CH: 10Hz ~ 500Hz (+0dB, -3dB)
Bridged Max output @ 4 ohms: 400W x 2 (A/B), @ 2 ohms: 200W x 2 (A/B)

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So any input would be great!

Questions that come to mind are:

1. The 6 speakers hookup to a 4 channel stereo or amp confuses me a bit but the already installed dash Pioneer stereo head unit does control all 6 speakers correctly with the Balance and Fader controls so I should be fine when I connect the amp to the factory speaker wiring harness behind the stereo.
I assume I will still have Balance and Fader controls through the head unit RCA's connected to the amp?

2. I've never owned a vehicle with SubWoofers but I do like them on a dance floor. A friend gave me a ride and he had SubWoofers in his trunk. He turned them on for me and it was fun .. for about 10 min. when I felt like my head would explode and ears were going to bleed..!
So I want to be able to turn off the SubWoofers, in fact I probably won't use them at all until I park and open the doors for a party dance outside the van mode.

The head unit has control/settings for SubWoofers but this is only if they are in place of the rear speakers.
I'm not sure the best way to add an off switch for the SubWoofers...

3. It surprises me that the head unit's built-in 50w amp will not get used. I guess it's considered a complete wimp next to the high power amp.
I wonder if there is an easy way to just use the built-in amp to drive the 6 speakers while driving and then if I park and want to go into party doors open mood, then switch to the separate amp and with SubWoofers...
Well that's probably out of the question.
Although perhaps I can use the built-in amp to power some exterior speakers...I guess too much trouble and they may not be loud enough to hear compared to the high power amp.

4. I'm guessing that I'll want to wire the SubWoofers @ 2ohms for more power and the 6 6x8 speakers will be 4 ohms....
I see the amp puts out more watts at 2 ohms...
No I'll have to read up on the amp manual is a lot to read through on all that.

5. The van has the largest that will fit and I've installed low power led bulbs in the dome and door lights.
I don't know if the power demand of the stereo will require installation of a large capacitor...
Even if it doesn't I guess you have to leave the engine running or the battery will die fairly quickly?

Thanks