Ditch the "tuned ports" all together and just make a baffle mounts yourself from mdf. Then you can size up to a more adaquate 6.75" or 6x9" speakers or ??? to get some ok bass. 5.25" drivers w/o a boat load of power will still sound like garbage. Check out the boxster wiki or do a search here for a complete guide on overhauling the Boxster's sound system including a template for the baffles.
Good luck
