While I have that same oem stereo, it was never hooked up when I bought the car (aftermarket system), so couldn't say if or what the factory amp setup is/was, but being you have the CD setup, have you looked at the back or what harnesses are there on yours? I would *think* any of the VR-4's have pretty much the same wiring regardless of what stereo they came with, but could be mistaken.
Are you looking to stay all oem, or have you thought about running an aftermarket amp with a converter (to run RCA's off speaker outputs)? The biggest challenge to that though is if you don't have one of those auto on amps (that come on with either the hi or low input signal) then finding a 12V remote source can be challenging. Least that's how it was in my last jeep WK, as it was all 6V signals...Ended up just making a switch to do it manually. Running an older punch 150 that required a remote.
But wait a second, these had power antennas, so that probably wouldn't be hard them to just tap off that line.