While I agree with the anti-Quart sentiment, I have to respectfully disagree with the comment about lack of midbass. I recently listened to a set of PSC-316's in a Boxster with the 4/tweet in the dash and the six in the door. The midbass (and bass) was absolutely amazing. I know the installer who did the job and he's adament about the Quarts having a solid enclosure behind them. Granted, as was alluded to, the tweeters were attenuated and a bit of equalization was used. The system really did sound quite nice and the tuning really smoothed out the "Quart edge". I too have been anti-Quart for the last decade, but I'm pretty sure I'm going to do the same system in my Supra since it won't require hacking up the door. The only drawback I see to the 3 way system is the 350 Hz x-over point - I'd like to see it closer to 250 Hz for my application so I may have to modify it once the install is done. Back in the day when I used to really be into this stuff (I competed w/ my Camaro and my M3), I had a similar setup in my Camaro. I'm typically against anything other than a sub being placed behind the listener, but a 250 Hz upper limit w/ a 12 db slope seemed to work pretty darn well and didn't jack with imaging. Of course, this was A) in a 1990 Camaro w/ a perfectly flat dash, and B) was with all Boston Pro speakers.
I'll be sure to let everyone know how the setup works out.
SP