FrankeeD. Are you using this system for movies as well? If this system is for music only and you are considering running without a sub, move up to the M80. The M80 delivers noticeably more bass. So much so, that on a lot of music, I can't hear any difference between just the M80 and the M80 + sub. Where the difference starts to show is stuff like Pipe organ where you get significant content in the 20-35Hz range.
The M80 also has a subtly better mid/upper range. They give music a more open sound: just a little closer to the real thing.
If you watch movies a lot as well, a sub will make a big difference for those movies that have a lot of content at 35Hz and below.
