I've been very happy with aftermarket tweeters in the stock location. I just installed a set of Focal K2Ps this weekend and I have a bracing bar that runs behind the stock location screwed into the back of the tweeter, which allows for excellent aiming through the stock grill.
You shouldn't have to run your own active crossover to find a decent component set that will include a gain adjustment for the tweeter. I run the Focals at -4db for perfect balance on my sensitive ears.