The analog idea is a good one. That's a way I had not considered. I've seen a few circuits (something called variable gain pre-amp or automatic controlled gain preamp) The noise and frequency response of that device worry me though.
An other difficulty is to create the -15V (or -12V would be enough) used by the op-amps (at least, for the one I've looked at so far). Do you know an easy way of creating a +12V/-12V in a car. I'll read on and keep you informed, as it is a long time wish for some users.

Best regards

Elperepat