You sir, are 100% correct. The OEM amplifier in the 440-watt
Harman Kardon® premium audio system is integrated with the ABS & the Vehicle Dynamics Control (VDC).
For those that may not know, VDC is an electronic stability control that utilizes sensors which constantly monitor wheel speeds, steering angle, brake pressure, vehicle yaw rate and lateral g-forces. If VDC detects a difference between the driver’s intended path and the one the vehicle is actually taking, VDC applies braking power and/or reduces engine torque to help correct vehicle path. The Traction Control System (TCS) is part of the VDC and it also incorporates an all-wheel, all-speed traction control system which senses a loss of traction and applies braking force to the slipping wheel or wheels as necessary to maintain vehicle motion.
So, it may be better to install an aftermarket amp that is run with RCA outs from the head unit to RCA inputs on the amp and then run all new speaker wire (14 AWG OFC or 12 AWG OFC) to your separate tweeters and woofers on your aftermarket speakers in your front doors while running the same gauge to the aftermarket coaxial or separate speakers in your rear doors.
If you decide to go with a 5-channel amp instead of a 4-channel amp, you can run new speaker wires to your OEM sub as well. I'd highly recommend replacing the OEM sub with the Pioneer TS-SW2002D2 8-inch Shallow-Mount Subwoofer. I just replaced the blown OEM sub with the Pioneer today. Honestly, I wouldn't want to run new speaker wires to the sub because you're going to have to take out almost all of the panels and trim work in the cargo area of the outback and part of the backseat to get at all that ridiculously thin gauge OEM wire. That may be another reason people can't get behind the OEM sub; the driver sucks, the wiring sucks, and you need to add sound deadening material behind the driver. That is a lot of work but anything worth doing is worth doing right, right?
I hope this helps anyone looking to mod or replace their OEM 440-watt 9-speaker Harman Kardon® premium audio system with 8-channel amplifier/equalizer, Digital Signal Processing (DSP),Dual Voice Coil (DVC) subwoofer, MP3/WMA capability and Speed-Sensitive Auto Volume Control (SVC)
Cheers