If the AX's arre just for fun, then get the PSS9's. I have the JIC's and they are significantly stiffer with the medium spring package than the PSS9's. I haven't driven a Boxster with PSS9's on the track, but I have driven one on the street and it was softer. Soft is not necessarily a bad thing for AX's, just depends on a lot of other factors like tires, weight, weight distribution, anti-roll bar stiffness, track smoothness, brakes and horsepower to name a few. Nice thing about the JIC's is that you can easily change the ride height for corner balancing without changing the stroke or spring rate.
CW