Lexus Subwoofer Amp is Playing Dead

Car: 99 Lexus SC400 Audio: Stock Nakamichi Premium Installing an IPOD between the headunit and the factory amps. The system is balanced, so their is 1 signal ground and 4 positive leads on the Nakamichi. Tied HU signal ground to iPOD negative leads and was able to hear sound through all four speakers (Front- Left/Right, Rear- Left/Right). Same signal for front and rear. The only problem right now was that (A) Stock Volume control isn't working as it would in a balanced SC430 Mark Levinson system and (B) Most importantly, the subwoofer amp is completely silent (playing dead). Obviously (B), jeopardizes the complete setup in the absence of bass. Admitedly, my Soundgate AVM2 Level Matching device hasn't arrived, so the gain is low due to the low voltage of an iPOD. Would the AVM2 solve my issues? Why is the subwoofer amp quiet? Attached are the diagrams for the NAK unit. Any help is greatly appreciated.

To clarify this was a direct wire test, so there wasn't any ground loop isolators/decouplers, switches/relays, or level converters. This should assist in troubleshooting before installing the complete setup.

98% Sure the voltage wasn't large ebough to drive the low impedance (1 ohm) of the subwoofer amp. This means the AVM2 "Should" solve issue (B) Any thoughts? What about issue (A) using stock volume knob. Any way to tap the AVM2 (Gain "Volume") Pentiometer to the Lexus Vol Pentiometer?