The serial cable supplied will work directly on the back of the empeg itself, but not on the sled. One is DTE, one is DCE. You'll need to use a null-modem adaptor with the cable in order to use it with the sled.

This is not really a good idea anyway - the sled also has other empeg-related signals on some of it's serial port connections, (eg RA, and dimmer), and you want to be sure that these aren't connected directly to your PC. You could wire your own cable to be sure - you only need TxD, RxD and Gnd, but it's easier just to use the serial port on the back of the empeg itself.