Dave,
The brightness for me is reminiscent of the brightness of a B&W loudspeaker. It's clear, the high end is definitely there, but it won't overwhelm you. To my ears, ones which were used to Alpine speakers, these are much superior in performance. But note, I do not have the coaxial speakers. I have 6.5" and 5.25" monopoles in the front and back doors respectively. Also, I have a pair of stock 1" tweeters in the front doors (in front of the window), and I'm certain that enhances the brightness I get. (I heard the MB-Q's without these tweeters when they were first installed, and they were the best door speakers I'd heard to date, if that helps.)
Where the heck is Zumbo when you need him?