I think using a cheater plug is fine for isolating the component causing the ground loop, but you should remember that the cheater plug is defeating the safety ground. If a short to the chassis occurs within the player (same voltage as in the amp), you risk completing the circuit with your body the next time you touch the player.
Note that if the signal ground is connected to the chassis safety ground of the connected components, then as long as the interconnect cables are in place the safety ground of a connected component will be used.
If you can not eliminate the ground loop, then isolation transformers are the best solution to break the loop and quiet the hum. Jensen makes the iso-max line.
Here's an article for more info: http://www.epanorama.net/documents/groundloop/problem_solving.html