Boxster's need and love negative camber just like any strut-based suspension! The stock set up maxes out at around -1deg camber in front but the car really needs much, much more.
A good starting point for a track-only setup is -3.0deg camber in front (where you go from there depends on driving technique, tire selection, tire temps, tire wear, etc.), maybe 0.5deg less camber in the rear, 1/16 toe (for stability, zero toe can feel "darty" but is generally faster), then add as much caster as you can get.
Of course, you'll need height adjustable coilovers, a set of GT-3 front adjustable lower control arms, adjustable front/rear drop links, and adjustable rear toe arms to reach this setup. Might as well throw in a set of sway bars while you're at it (GT-3 front, Tarett rear).
Have a race shop do the alignment and corner balance. You'll also need to keep an eye on air pressures to keep everything in balance.
This is a very good reference page:
HELPFUL HINT: Porsche Boxster Suspension Setup - Stock, BSX, BSR - GSR Autosport Community
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