Wow, exact same problem here with my 2006 CS, short shifter, 20,000 miles. Grinding downshifts into second, and lately grinding upshifts. The other gears are fine. My shifting technique is not the issue. I am no mechanic but it sure seems like damaged syncros. Car has never been tracked or abused.

My car has been in the Porsche dealership shop for 2 weeks. The cables were replaced, but that was not the problem. As of today the transmission is out, but the shop cannot "open it up" since their is no tech info on this and apparently the mechanics are not allowed to work on it. The alternative may be a new transmission. I will find out tommorrow.

Keep us posted on how your problem resolves, I will do the same.