A few observations on the system design, tuning and the like: I initially bridged the XD400/4 to provide 200 watts to each Illusion Audio C6, but I was getting some harsh bass notes occasionally that almost sounded like bottoming-out, primarily on the left side. Concerned they were getting too much power (although the gains were at minimum), I decided to just run 2 channels at 85 watts to each midbass. Surprisingly, I actually got an identical response (with gains optimized on 0 db tones), so the problem was either the physical properties of the door or something odd in the factory system. The interior door skin is plastic instead of sheet metal, so the lack of rigidity may be causing the problem. I deadened it as much as possible, but the problem remained. I decided to continue powering the C6's with the 85 watts since I'm getting plenty of output, and I've been able to tame the problem with EQ and raising the crossover to 75hz at 24db L/R.
I previously complained about the Ford head unit's audio performance, but it improved a bit with the LC2i providing high/low conversion. It still lacks some resolution, particularly on more complicated musical passages, but it's livable. The Fiio M11 is obviously much better, but I've found it difficult to use while driving, which to me defeats the purpose. I'd rather have the convenience, functionality and added safety of using the factory system and lose the resolution of the M11.
TWK-88: easy to use, does the job. Wish it had speaker-level inputs and signal sensing. Also would like maybe 14-15 bands of parametric EQ per channel instead of 10. 10 bands for each speaker in an all-active system sounds sufficient, but a few more bands would still be handy. I wanted to go all JL for amplification/processing, but if I was starting over, I'd go Helix or Zapco for the DSP. That said, I've been able to get it tuned really well. It's just taken some time to get there.
Illusion Audio C3CX's: In my particular application, with a-pillars and nearly on-axis mounting, the imaging is unreal. Still wish they came with some cool factory grills, though....
Weather's been bad lately, but hope to get the ST cleaned up for some final install pics soon and then call this project done!