Thought I'd give a quick update for those that come later with similar problem.
I ended up buying the bypass harnesses and quickly bypassing the factory amp and boom, success. I purchased this from Crutchfield: Metra 70-5002C Wire Harness for the 1996 Mustang GT (non-Mach 460). After researching on the internet again, I finally realized these connect to the ones that are on the right side (a gray and black one) behind the head unit. No idea why I didn't realize these earlier. The other good tip I had read was to make sure to connect the 2 ground wires first, and of course, disconnecting the negative battery terminal.
Oh, I also bought the Posi-Product screw-on car stereo connectors. They are friggin' awesome. ;o) Posi-Products Car Stereo Connectors 16 connectors for installing a new car stereo at Crutchfield.com
Next up is a decent pair of speakers (already purchased).
Thx again for this forum!
PS. With the factory amp disconnected, is it okay to just leave there? Seems like it would be almost impossible to get that thing out although I haven't looked at closely enough either.