I just finished running it on mine ... I used the Radio Smack Analogue (for the Brits) SPL Meter (33-2050) ... I found a mic calibration for this meter, but it sure didn't match mine.

When I downloaded the demo version of SpectraLAB, it came with a calibration file for that particular mic built-in. What software did you use?

There is an issue in doing this RTA work that I haven't yet resolved, I'm wondering how you felt about it:

At first I thought the mic's exact position in the vehicle wasn't important as long as it was somewhere close to the driver's seat. That's still true in terms of its height placement and left-right placement in my car. But I noticed that there were significant differences as I moved it forwards and backwards in the cabin. It seems that standing waves resulting from the differences between the front speakers and the rear speakers can make a significant difference in the frequency plot. As you move the mic forward and backward, you can see sharp peaks and valleys appear and disappear.

Other than completely crossing over all speakers so that they don't ever intrude on each other's frequency bands (impractical in my car's setup without some additional expense for different kinds of speakers), is there any way around this?

And of course, Greg, I'm sure that you've discovered that (a) it's impossible to get it perfectly flat, and (b) anything close to a perfectly flat response line doesn't even sound that good. The RTA is a "baseline" from which you tweak to taste.

I've found that I like the way Genixia's Bass/Treble controls work off of the EQ. I can use the first eight bands for all of my RTA corrections and leave bands 9 and 10 open for Genixia's code. Then I can increase the bass and treble in Hijack to give the overall response a decent amount of punch. Of course, then I have to make sure to keep the volume control below -6db to prevent clipping.