I appreciate the response, but I included it in the original request that I dont have the Bose system, as that seems to make a huge difference in where you tap in. As i've been going along today preparing for this install, here is other info i've gathered:
ITEM WIRE COLOR LOCATION
Left Front Speaker (+/-) // blue - brown/blue // radio, green 16 pin plug, pins 1 - 9
Right Front Speaker (+/-) // yellow - yellow/black // radio, green 16 pin plug, pins 2 - 10
Left Rear Speaker (+/-) // green - green/black // radio, green 16 pin plug, pins 3 - 11
Right Rear Speaker (+/-) // white - blue/black // radio, green 16 pin plug, pins 4 - 12
I was hoping to just tap in at one of the plugs in or near the BCM, which may be possible, I just don't know. A tip that I got is to pull the B-Pillar panel (between front & rear doors), pull back or cut the tape on the wires going into the rear door to look for the speaker wires. It should be the ONLY TWISTED PAIR in the bundle. I may go this route since I don't know if there is an amp after the green 16 pin plug at the radio.
Forgot to mention which power source I used for the amp's remote on....
If you look under the driver's side dash between the brake pedal and parking brake, you'll see the fuse/relay box (it's about 6" x 10" and has a smooth black plastic cover, just like on the GMT-900's). Pry the clasps on each side to remove. On my SLT there are three main banks, left to right, with the first being unoccupied (see attached pic). The slots within first bank are labeled 1-20, though only 11 actually have male connectors. I used my tester to determine the following: #'s 7 & 17 are constant 12v power [always on], #'s 10 & 11 are grounds, and #8 is the RAP [retained accessory power] ignition signal wire (again, see attached pic)
For newbies, RAP powers on with the key rotated to the first position and remains on until the ignition is turned completely off AND the driver's door is opened, just like the factory radio.