System upgrade plan - Factory Head unit remains....

[Studio472]

I have a 2.5S w/ the "basic" head unit. At this time, replacing the HU is not an option.

Here is my plan...

- Power Kenwood KAC-8103D MONO block Amp w/ remote control KCA-WR10 Bass Knob - Having Frequency & volume control (at the amp level) will make up for a lack of head unit...for now.
- Sub - Single JL 12 W3v2 in a sealed box
- Will tap rear deck speakers for HI level input, the amp has a HI/LO converter (yes I know it won't sound as good as RCA's at line level - this is the price I pay for NOT upgrading the HU) Eventually will go with a nav unit...
- Do not plan on replacing any of the factory speakers, (other than the muddy rears, I really like the mids / hights)
- Plan on adding bass blockers to the rears (after the Hi/Low)

Questions...

- Where should I connect the trigger wire for the amp? Does anyone know the color codes for the wires on the HU?
- Is there any "Low" level I can tap directly out of the factory HU?

I'm open to your suggestions and ideas...

I DO own the sub. Do not own the amp yet...