SVS 20-39PCi vs Earthquake Super Nova MKIV 15P

A friend of mine (who got me into hometheaters...Damn Him!) brought over his Earthquake 15P 580w Sub over to compare it against my SVS. We hooked them both up to my receiver with a y-cable and would turn each one off to try and compare. When we did he would say "Hear the difference?" Honestly I couldn't. I definitely do not have a discerning ear but I know what I think sounds good. When I asked him what he thought was better he said it is just the overall quality and the bass was a bit tighter. Anyone want to clue me in on what I should have been focusing in on when comparing the two subs. We listened to some of his CD's I think the Chemical Brothers, and played some DVD's like TS2 and TPM.
I don't think there was all that much difference in sound but just want to hear if anyone has an opinion on this. I definitely don't think there was an $1300 difference in sound. Makes me sleep better at night knowing I have a sub that sounds as good as a $2000 sub Atleast I think so.
Ken