Headphones

I’m asking for suggestions to upgrade my current headphones, something that would be a noticeable sonic improvement. I would use them for checking mixes and tracking. Those that interest me are the ATH-M50, Sennheiser 600, or Beyerdynamic DT-770 or 880. I own the following: AKG 240 – These are my favorite, they sound natural. Shure SRH440 – OK but too crisp. Bose Quiet Comfort 2 – Horrid, have too much bass.
Thanks for any suggestions.

I highly recommend the Beyerdynamics. DT-770s are best for tracking with just superb isolation. DT-990s are best for control-room monitor substitutes (my favorite headphones of all time) but are completely open. DT-880s are somewhere in-between.
JP
edit - sorry, not awake... just re-read your post...