Your comp speaker out is 1/8th inch, not 1/4 inch. So you would need a cable that is either 1/8th male at one end and 1/4 male at the other or same diameter at both ends and a corresponding adapter at one of the ends (more like 1/8th to 1/4 adapter to plug into the Line 6 as it's going to be the stronger jack) to handle the weight)