I get a slight grinding feeling when the transmission is cold. This feeling has been increasing over the past couple of years. Any ideas?

 

try changing the fluid and letting the car warm up

 

This.

Until it warms up try shifting slowly around 4K

 

redline MT90

 

S2K gearboxes are grindy when cold, everyone I know with them agrees.
They also clunk a lot when cold.

Try replacing MTF, use Honda OEM.

 

Most are notchy when cold. Try changing trans fluid as mentioned if you haven't done so recently.
I recently switched from Honda MTF to Amsoil and find it much better! Slightly notchier when cold but when warm night and day difference.