Okay, then that's abnormal operation if even with the sub trim on the receiver that high the sub still cuts out. It seems unlikely that the cable was damaged and is so intermittent that the sub isn't getting enough voltage, but as you suggested move the sub enough so that you can try the shorter cable.
Another remote possibility is that the 5960 sub output is defective(ordinarily it can put out far more than enough). Connect your player analog output directly to the sub as an experiment(if that isn't what you already referred to as having been tried)to see if the player output voltage keeps it awake. Otherwise contact Axiom directly, since the sub amp may need to be replaced.
