I'm considering a center-channel speaker in the location of the sunglasses holder (front ceiling near the rear-view mirror).

Sounds incredibly good to me, if you've got the room. How big a speaker could you put in there? Give serious thought to a coaxial speaker, something around 5" with built in tweeter.

I don't know what your "sunglasses holder" looks like or how big it is or how easy it will be to get wiring there (inside the headliner?).

tanstaafl.

"There Ain't No Such Thing As A Free Lunch"