You need a guide port adaptor for the other end - a lot of people use the Shoestring GPUSB interface device
http://www.store.shoestringastronomy...roducts_gp.htm
You can also get the cables from him with the correct wiring for the EQ6 autoguide port - or follow the instructions on his site to make your own.
I don't believe a USB to serial converter will work with the autoguide port.