I got the ATH-M50xBL for that same purpose. First impression was "oh, bass!", but it sure makes me miss the HD600, so I don't really last long in the studio with it. Things just seem to sound so much more harsh on the ATH-M50 in comparison, but of course after a few hours you get used to it.
Yeah, that doesn't surprise me... I am not expecting the M50 to be a big standout, just a reliable set of headphones for whenever we have a guest or I am just in the mood for something different. I thought it would be cool to keep something like the M50 in my collection just to serve as a baseline comparison headphone since it has such a great reputation at its price point and has been a bit of a milestone product for so many years now.
For studio work, I would strongly recommend the HD600 and the Focal Spirit Pro. I haven't tried the Sony MDR-7520 yet, but I just got the Focal Spirit Pro a week ago. If you can get past the fit issues, the Spirit Pro is an amazing headphone. I don't think it gets any better than that for studio work. I do think the HD600 has an important role to play in the studio as well, and of course the comfort and lack of fatigue combine to make the HD600 a very special headphone as well.