Just a heads up. Some audio cables are what they call "attenuation" cables. These cables look exactly like a standard 1/8" mono cable. The difference is that the "attenuation" cable has a resistor built into it. Has something to do with special audio equipment.

If your 1/8" mono audio cable does not work it may be an "attenuation" cable. You can easily check it with a muli meter. Check the Resistance from one end of the cable to the other for the positive and the negative pins. If the meter shows resistance then it won't work for you.