Welcome Pete,
I can't comment on the 683's, never heard them. All I can say is that I was >< close to purchasing some brand new 703's at a local high end AV dealer. Luckily I was able to listen to some m60's at the time and boy was I glad I did not spend the extra money. To me the m60's sounded better overall than the 703's, if that helps.
Also keep in mind, if you order from Axiom's outlet you save 10% off the regular prices.
ps: I now own the m80's which are dynamite.
For the small difference between 60's and 80's, you might want to consider 80's as well to avoid upgradeitis in the future.
The m60's are fabulous speakers though...
