I think your problem is that probably the monster cable you bought is an insert cable which means it has one left and one right plug on one end and a stereo ring tip sleeve single quarter inch jack on the other end. You can tell this if the single jack on one end has two black thin bands running around the jack rather than the single ring on each of the other two jacks.
If this is the case, you are trying to plug this into a jack which is not intended for this stereo type of plug. In this case you are better off using two cables with one plug going into one channel panned left and the other plug going into another channel panned to the right.....or if you mixer has stereo input channels, you can plug one into left and one into right and control from one volume control and usually a pan knob.
I hope I didn't confuse you even more!
George Kaye
Kaye's Music Scene
Reseda, california