As far as referencing
I think that you can use phones to listen for detail, if what you have is a less than perfect monitoring setup (like a lot of us do). I'm sure a pro wouldn't have to resort to it, because they have better monitors in a better space and they know them more thoroughly. You can't use headphones for mixing, because you get an unnatural sounding bass in phones, but more importantly, the stereo field is exaggerated.
If you're listening for detail in a mix or even an individual track (not
while you're tracking), my vote is always
Beyer DT-770. Doesn't mean you'll like them.
For tracking, I don't know enough to give a valid opinion.
I'm with Harvey on the harsh highs of 7506's, plus I think they have a hyped bass, too.
But lots of people use them, so my opinion must be in the minority.