I purchased the ZThin cable from serialio.com for my SL5500, which it worked quite well on it's a great alternative to the bulky Sharp offering.
It will also work with the SL-6000L BUT you have to cut off the little "ears" either side of the actual connector in order to fit it to the 6K. Apparently they thought we would be swinging our Zaurii around our heads like a bolo as I can see no other reason for the connector overkill.
The cable still works just great on the 5500 too. It works on either device with the keyboard either extended or closed.
Hope this helps,
Dirk Prusok