found these while googling
1.
http://www.rahul.net/dennisp/boxster/boxster-mods-engine.shtml
2. 34HP Dyno Developed Tuning Kit ( Boxster sport muffler, Boxster Headers, BMC F1 air filter, Piggyback Program or German DME Remapping ). Consists of Fabspeed Exhaust and Fabspeed German ECU DME Remapping service. Source: Dyno proven power - you can feel.
http://www.fabspeed.com/boxster.html
3. RennSport - has graphs and dyno tests shown, but the gains are still fairly modest.
http://www.rennsportsystems.com/996-Boxster.html
4. Interesting write up from a forum, with some thoughts attributed to Alois Ruf on Boxster mods (and 996's). Some good thoughts on the interaction between systems and how you can actually upset the balance by changing a single component. Only read the first entry - it runs on a wile after that. The Ruf pricetag: 27,000 euros, a bit steep for me.
http://www.theautobahn.com/forum/archive/index.php/t-5034.html
still no easy answers - but it's gotta be out there somewhere.