when it comes to speakers, there are a lot better things than MTX out there... TC Sounds used to be pretty good, however they switched to the name AudioPluse then went under. You could try Acoustic Elegence, they sell low distortion mid to low Xmax drivers with fairly high sensitivities. In english: they're loud and sound good doing it.
Acoustic Elegance • View topic - Preliminary specs on new 6.5?
If he ever finishes it... In the mean time, look to pro audio drivers. They get ridiculously loud with less power and still sound good.
In the high end (meaning tweeters)... Seas, Peerless, Vifa all make decent speakers. Ideally you'd try something with a higher sensitivity like a ribbon tweeter but they're almost too fragile for the car environment.
