I still say that his money will be better spent now on a (much) better sub than an amp. That way you'll definitely get better explosions.
Absolutely. That made a vast improvement for me in the overall sound and "enjoyability".
As JohnK always says, unused headroom is exactly that: a waste of all resources. You know that he'll chime in later.
I'd also say that your room size may play a factor here. I've got under 2K cubic feet in my room and my Onkyo receiver is plenty loud enough thank you. Large rooms - I mean huge here - are obviously different animals, and would need more assistance/power. Simple physics.
I really don't understand some of the folks here who have small rooms and seem to want to continually jeopardize their hearing. Mine's at risk from health treatments and I've been suffering with tinnitus for a over year now because of a single treatment of a drug last summer. It's really very uncomfortable. Be reasonable and protect your hearing. </dismounts soapbox>