First off what are they (besides the big round things in the front of the 755), and how do they work in an amp?

Second question, is there an up-side / down-side to having "5 individual toroidal transformers, 5 individual power supplies, 5 individual amplifiers" vs. the way outlaw had the 755 amp setup. The reason I ask, I saw an add for the following amp :

http://www.sherbourn.com/products/5_5210.php
I just wondered what the logic behind this was. Thanks for the help.