I hooked up the amp and head unit first and did some preliminary listening as I was replacing the speakers.
The factory dash speakers, I would classify as junk. Comparing those with the replacement, there was a huge improvement. I can certainly understand how most people would be pleased with replacing the dash speakers. There is finally some bass where there was none before and much clearer highs. However, in hindsight, the dash speakers were a totally unnecessary step as they are trounced by the component speakers and add very little to the overall sound quality of the final product.
In comparing the door speakers, which are just a subwoofer in the stock system, I was stunned at just how good they really are with proper power delivery and matched with the component tweeters and component crossovers. I believe it is due to the large voice coil and magnet for the small size of the speaker, and that they were specifically designed for that enclosure. They are 2 ohm speakers, which will draw a little more power from the amp, but modern amps should handle them with no problem. The sound was a bit shallow in the upper bass, but punchier in the lower bass. However, at this point I had already converted one side so I was committed to do the other. The component woofers from the kit are very good as well, not as punchy in the lower bass as the factory subwoofer, but have a much broader sound. Anyone who wants the most bang-for-buck might consider only the HT25 tweeters and component crossovers that came in the kit and save themselves a bunch of work by not replacing the subwoofers.
Overall, the final product has met with my expectations. The bass is very good for a system without a true subwoofer. Playing DJ Magic Mike's Ultimate Subwoofer Test won't rattle the windows, but you will feel it in your chest, and it will find anything that vibrates in your car. The drum beats from Fanfare for the Common Man from the IASCA test CD are very powerful and very convincing.
The tweeters are wonderful, and I don't heap praise lightly. They are among the best that I have heard. Very clear, bright, detailed, and without a trace of sibilance. Female vocals really come to life. The trumpet attacks on John Williams Duel of the Fates is spot on and will have you grinning. You will be searching your music collection for high quality recordings.
Regardless of the genre of music that you enjoy, jamming to Stevie Ray, Country, or Classical, a system that is musically accurate will be able to play it back as the producers intended. It's not that hard or expensive. It just takes some very careful planning and your Boxster can have the sound quality that is as luxurious as the brand deserves.