1, yes if you have any extra speakers they would work there. same company sounds the best, "all matched up specs wise"

2, yes definetely, i have a 6.1 amp running my 5.1 set up and it been doing this for about a year, going to get 6.1 in a week or so. and it would have the same power to each channel.

3, mostly pretection from people poking the tweeters and woofers. on all my speakers i have the grills off, maybe its just my speakers but they all sound better with it off. "and look way cooler"

4, coax like tv cable or a digital coax? if its digital coax then it goes from dvd coax out to receiver coax in. if its regular cable coax, then its no use if you already have cable going to your tv. if you have audio output on your tv you run that into your receiver.

5.its for component video switching. you run all your components into the amp, then it sends it all to the tv with 1 connection. instead of you using video 1, 2 , and 3, on your tv you can have it all on vid 1.