The EQS is a powerful bit of kit. I had an Alpine 7998 used the EQ in that to death, and my mate had an H700 so have played with EQ's for far longer than is healthy! Do you have access to an RTA machine at all?
If we can get a frequency curve in the car then we will have a good basis as a start point. I have a few CD's that can be used to set the car up, testing sound stage (height, depth and width), frequency response, sibilence, extension and so on. By no means a pro but spent a lot of time listening to a lot of cars, so am happy to help if I can.
Am missing my sounds....