Well Matt, if you actually read the post that I made, I mentioned grounding the amp better than it was grounded. Perhaps you didn't read into things, but where do you ground the amp? To the subframe of the car? (at least that's the preferred method) And where does the car ground to? Yes... that's right. The negative terminal of the batt. So, connecting another, larger wire from the frame will in fact give a more solid connection to ground.

Grounding the engine block will assist with the grounding of the alternator, which grounds through it's casing. (which is attached to the engine with bolts, which conduct electricity)

Now then, dispite what you may believe, this does and will help. And if it is, as you seem to believe, some manner of snake oil, then at least it's not expensive snake oil. He's looking at a total cost of about $10 in parts (highly over-estimated). So instead of suggesting he spends $100+ that he doesn't need to spend, I suggested the $10 route first. 1/10th of the cost that can, and will, solve at least a part of this problem.