I've done the PCNA kit and was happy with the result - with the caveat of recommending addition of tweeters as well. You can see
my installation on the Boxster hacks site if you're interested.
Note: One change to a step I recommend in the site instructions is to avoid using the hot melt to tack the cables routed along the lip of the storage compartment - I later found out that apparently it gets hot enough under the rear window on a summer day for the glue to become liquid again and seep into the engine cover carpeting. Stick with the Porsche-supplied wire clips (if you can figure out how to use them w/out nicking the wires ) to avoid this.
I also later modified my install to add tweeters in parallel to improve the highs over the stock kit.
Let me know if you have any questions on the material posted, etc.