I did this in my boxster S as the speakers were not installed. The upgrade was night and day. I didn't use this company but the speakers and the parts look the same. I paid around 200.00 for mine and loved them. I also used a little poly fill in the open space to give the speakers a little more push. Here is a link for the install plan on spending an hour or so.
Also take the car to any good high end stereo show who work with European cars and they can "upgrade" your system to sounds as you'd like I am sure as well as keep it either custom or factory to your likes or dislikes.
Even though this post is old, I'll add my experience recently buying a Boxster in case other future buyers are interested.
When test driving various boxster options, I happen to try the base sound, a car with sound package plus option, and a car that had itself the Bose option.
While sound package plus gives you more speakers, I felt that it did not give you superior sound, just more of it. I see no reason to get the sound package plus option, the price tag of $700 is a bit rude.
The Bose sound option was very good. But of course is it $1690 more to the car. Was that amount worth it to me? No.
In the end I decided I can provide for future sound upgrades on my own (if so desired) better and cheaper than the Porsche options.