Check out post on FA. search on Bose system, there have been some folks who at min. swapped out the tweeters for improved sound. It goes into the issues of our Bose low ohm speakers and the troubles with upgrading them, etc.
All 4 door speakers are 7" speakers with an awkward mouting design. I replaced all mine with Infinity Kappa Components in the front and 2-ways in the back. Sounds better, but then again, I have aftermarket amps powering them too. Like dmako said, in Fresh Alloy, someone replaced the tweeters only with the same set I have, powered by the stock Bose amp and liked the results. He then replaced the mid-bass speakers as well. You will definately have to drill holes to make the aftermarket speakers fit. Crutchfield says the the Infinity's will drop in, but they don't. I've sent them an e-mail notifiying them of the error and they said their techs will look into it. Never heard back from them since.