The neutral line is tied to ground at the service entrance at most homes. So in some products, the hot and neutral are treated differently, such as the hot line has the fuse. I don't own it, so I can say if this product is polarized. The grounding is mainly a safety issue. But most metal products require a ground for safety in case there a failure (e.g. short). Grounding can also make a difference in audio products. If not grounded, or incorrectly grounded, you could get a ground loop. That will add hum to the speaker. Yes, you can power more than one amplifier off of one power supply as long as the current drawn from all three amplifiers is not greater than the current rating of the power supply.