Shadrach74,
Here's the answer to all of your header/cat exhaust woes . A set of custom fabricated headers and precats from M&M Exhaust in Germany. They feature longer, equal length primaries with 2.25 diameter piping, along with an F1 style merge collector and HJS 200 cell trimetal cats - beautifully made from T316 stainless steel . Net hp increase - probably somewhere in the range of 8 to 10 hp at the wheel . Cost - approximately $3800 . Aggregate cost- about $300 or so per hp .
http://www.fvd.us/us/en/Porsche-0/Boxster_986-13-41/-/-/item/item_details/VID_57324217-VCD_35203588-gid_28-sort_4-display_50-item_BES98601200S/EXHAUST_-_Tuning_-_Headers-BES98601200S-Sport_Headers_`Brombacher`__986_S_-04_with_200_cell_sport_catalytics.html