This is really sound advice... no pun intended If there is room in the mirror covers, you should test there as well... although if you choose that route you have to run speaker wires into the doorsJust pull the tweeters out and hang them where you want and listen. A little duct tape and/or safety wire. You can even play with rotating them.
Unless you are not in a position to adjust the tune to match ?
I'll go out on a limb and say it won't be $1600 better.