i do use the 4CM method to loop my rack to my gt8.

as for the USB midi cable, its diff from the regular instrument cable as it merely acts to pass data. u dont really have to go for such a high end one as speed transfer is not an issue. just get a regular usb midi cable from lowyat plaza around rm90 range. it gets the job done. i however never use it to transfer patches to my gt8 as i dont really see the point of doing so (plus, it isnt as user friendly as line6).