Michael,
Thanks for your interest. I'm running a Kenwood deck (top of the standard line, not Excelon), an Arc Audio 2100 amp for the fronts and a Arc 2050 bridged mono for the IDQ10 sub in the trunk. The fronts are 6 1/2 s high in the doors (mounted like yours, I forget which one of your vehicles) and 5 1/4 coaxs under the factory grills in the dash wired through a MBQ 3 way crossover. It sounds very good, but it seems the better it sounds, the more I expect of it.
I have the midrange up all the way on my Arc EQ and it just isn't quite there. I thinking of making custom door panels with Boston Pro or Focal Poly Kevlar 3-ways, with the mids and tweeters aimed towards the listening position.
GeneralBilly,
6 1/2s fit nicely in the doors, I didn't watch the depth of the speaker and ended up having to make a 1.5" spacer to keep the magnet from hitting the window when it rolls down. What you have described is certainly a modern sounding system, that was my goal too and then the car audio bug bit me and now I'm looking for audio perfection.
FWIW, I've read almost all the posts regarding w124 audio and Michael is certainly one of the experts on this subject, so if he says 4s and tweets sound great under the stock grill, I'd bet they do!!
Good luck and let us know how it turns out.