before you wrap everything up, here's another tip....
Fill the complete cavity behind the speakers (in the box) w/ poly-fil (like aquarium filter stuff or stuffing from a cheap pillow at Target). This will slow down the air flow making the speaker "act" like it's in a larger enclosure to help get some lower tones.
If you have an old pillow laying around the house, just cut it up, or buy a small cheap bed or decorative pillow at Target, Micheal's, Joann's (s/b $3.99 and under) and cut open. Pack the stuffing in loosely, but firmly (I know, clear as mud, right). Well how about... firm enough to not fall out when you remove the storage box, but loose enough to allow air flow
Filled cavities will help the sound. Again not a huge improvement, but another step along the way to improving the Boxster's sound system.
