Well first off, the HD595s are getting very dated by now. On top of that, you can save a bunch by getting a pair of HD555s and modding them to sound exactly the same if you're comfortable with that kind of thing (and if you lurk this forum you should be ^_^).
The other issue is that no matter what set of cans you get, the source has to be good enough. Discrete sound cards are definitely the way to go if you're willing to spend that much money on headphones in the first place as onboard makes almost all music sound muddy.
Gaming headsets are definitely an option if that's pretty much all you need them for, but before you buy make sure you are not going to use them for music because other than LAN sessions, their audio software often ruins music listening.
I would recommend getting a pair of HD555s as you can mod them, and they sound very good for the price. On top of that, with a Zalman mike (as you mentioned) they can double as a very good pair of gaming headphones as well. If you want something more comfortable, try the Audio Technica ATH-AD700, which I have heard are a little better for gaming purposes as well. Whatever you do, if you are serious about sound quality know that no amount of software fiddling is going to advance your experience as much as a discrete card so prioritize that (but make sure you don't go overboard by splurging and falling for some of these marketing scams).
BTW before you make you're decision make sure you either look around these forums (I'm pretty sure I've seen a bunch of threads like this before) or http://www.head-fi.org
for more information.