I wasn't able to get anyone on the phone (it directed me to leave a message and then said the mailbox was full and hung up on me, I was trying the tech line, maybe should have tried sales
) But I emailed them and they got back immediately.
Koni confirmed that the FSD works with 986 Boxster springs, either M030 sport or "regular" (did not ask about ROW springs but they are popular in the UK so I imagine yes). It is compatible with the Eibach Pro kit springs for Boxster, which Eibach doesn't make anymore, so there is no kit from Koni for Boxster that includes springs. Eibach does still appear to make the Pro-kit springs for 996 2WD variants, and I think that is what Koni offers with their FSD+Springs kit for 996. They are listed as lowering the car 1" front and rear.
From time to time a set of the 986 Eibach pro-kit comes available for sale - there was one on here a while back, new in-box.