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.
Let me know if you have any questions on the material posted, etc.