If I'm not mistaken, the EQ is controlled by the amp. The system automatically changes the curve depending on the type of music being played. My dealer was very helpful in trying to rectify the situation. First, they switched out the original radio with one from an S on the lot. When that didn't solve the problem, the regional rep got us a modified radio that supposedly was "mapped" with the EQ settings from the earlier Beta stereo.

What happened was interesting: The stereo sounded like the 92-93 systems for a few minutes, then the it sounded horrible after that. My suspicion is that the amp somehow overrode the head unit's modified settings.

Eventually I waited about two years and got it replaced for a final time before the warranty ran out. The one I have now sounds the best of all of them but still nowhere near the 92-93's.