Those are great cans! I recommend them all the time. However, I'm not at all surprised that you're disappointed in headphones' versatility if that's what you're using for producing and casual listening. The v-shaped frequency response can be really tiresome and the ath-m50s have a mid bass bump that makes mixing a lot harder than it should be. When you have the chance, I think you should get a nice pair of open headphones for comparison. No need to go all out on LCD-3s (maybe one day =)), something like sennheiser hd600 or hd650s would be really refreshing, I think.
OtterSlick also pointed out that the sub bass presence in speakers is capable of consuming your whole body rather than just your face. Speakers can make you feel like you're at a show watching a band perform, and headphones can't physically produce that feeling. Some do a pretty good job at giving the illusion that they can, though.