I have 6's, with the updated 7 tweeters. I think you can get these from a dealer for about $1200-$1500. Not exactly sure. But they really improve the top end of the 6's. So that closes the gap somewhat on the 7's. Then you still have cash left over for a sub.
I watch a lot of movies, and I don't miss the deep bass. Maybe if I stopped by Jameswei's house I'd reconsider...so take my comments here as never having heard a sub in my system.
All this said, I'd buy the 7's. They are a better speaker all around, especially if you main listening is music. The 8's are wonderful. I am trying to get the cash for them one day soon...
Also, I guess I should mention, what's the rest of your setup? Maybe improving sources, amps or cables and going with the 6's still might be a better option.
Sorry to waffle around here, but lots of varibles I guess.
Good luck !