Dermot,
If the lowered floors and removing the seat rails doesn’t get you low enough, you can try a bead or foam in place seat. I am 6’4” and recently ordered an SV with lowered floors and leather seats, this got me low enough. However, in my 2 previous S3s, I removed the driver’s seat completely and built a foam in place seat bottom, this effectively had my butt about an inch above the floor. The seat bottom was very comfortable, the seat back was just a 1” piece of foam, covered to match the seat bottom. For me the extra benefit of the custom seat bottom was I could create much more thigh support by extending the length past the chassis support bar.
Jim