E36 HK Stereo Problem: Location of Amps or processing unit?

Hi, All,
I own a 1998 328i with the Harmon Kardon stereo upgrade.
This system has a switch on the console that turns on and off some kind of spatial processing which boosts the bass and alters the "stereo
image" specifically for this model of car.
Recently I have had a problem where just the bass-boost and image "processing" switches on and off intermittently. The system works and sounds normal when it's working, so I know the problem is not a fuse or blown component. I suspect a loose connector, but I don't know the location of all of the components of the system.
I know about the in-dash head unit, of course, but are there seperate amplifiers? Is there some kind of processing unit seperate from the head unit?
Thanks for any info or hints!
Ken
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Wow, HK in an E36 is quite a rarity. I don't know, but the first place to look would be in the boot. As it is factory, then it may not be that easily spotted.

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