1990 300D Becker 1480

[2.5Turbo]

I've been contemplating upgrading parts of the sound system in my '90 300D 2.5T so I've been doing some research on the factory system. It has the standard 1480 head unit, but also has the active bass system (woofers in the front doors). I seem to remember reading somewhere that in 1990 only the 300D had the active bass system as standard equipment, and 300E didn't.

I know that later 124's had the 1432 radio which had the receiver and amplifiers in the trunk. The 1480 has amps in the head unit, but I've been reading that the active bass system uses an amp in the trunk. How exactly does the signal from the 1480 get to the amp, and what level is it? I saw some photos of the back of a 1480 on ebay and saw that there was a line out plug on the back, and they said it was an "optional line out module". Is the active bass amp driven from this? I really don't want to have to go through the trouble of pulling the console wood and yanking the radio to find out...plus I'm currently 2500 miles away from the car until May