Originally Posted by DeFKnoL
Now I am thinking of a way to get my highs by either adding in an aftermarket tweeter in the sails (this means cutting, yuck!) or on top of the dash near the window.
LOL, the only other thing you will need then is some 6x9s resting on top of the rear deck to give you the full sound experience! (sorry, couldn't resist)
But seriously, just adding tweeters can be an improvement, if integrated and positioned correctly. The sails would be the best position (keeping them as close to the mids as possible), and there are replacement sail pieces with tweeter mounts you can order from the dealer.
However, I seriously doubt that you will be able to give them enough power from the head unit, and I'm also not sure that you will be able to run the tweeter parallel to the mid without adding to much stress on the internal amp. Also remember that you will have to add an in-line resistor to protect the tweeter from the lower frequencies.
I am not too familiar with aftermarket speaker and amp options for your system, so I will let some other speak for that.