Nilch,
An I/O cable for a sl-5500/5600 will connect a 6000 to a pc without the cradle (at least in Win2K, WinXP and Fedora Linux). The difference is that the connector in the bottom of a 6000 is turned 180degs from a 5500/5600 (the physical connector, not the connector pinout). However, unlike a SerialIO thincable, you can't use the keyboard on the 6000 while it is plugged in.