Hi, no problem. EQ software on PC, I use Equaliser APO, it's free and completely integrates with the windows audio chain, so anything you listen to through any players or internet browsers will have the EQ applied - it's probably the most used EQ solution for PC, it's a very versatile & powerful program, however it can be a bit confusing until you understand the logic of how it's put together.......if you find Equaliser APO too confusing to use to start with, then install PEACE, which is an "add-on" to Equaliser APO and gives you a graphical interface that most people find easier to start with. So you'd install Equaliser APO first, and then you'd install PEACE - they work together.
Beyerdynamics, I've not heard particularly good things about them, treble in these headphones can be quite piercing and they're not particularly good when EQ'd from the reviews I've seen (well I've seen Amir's review on here of a Beyerdynamic, I've not researched it, so just judging from that.).
AKG K371 you mention (a closed back headphone). That's a good headphone, with impressive bass, and just a slightly below perfect treble which can be almost completely fixed with EQ. The problem with K371 is that it probably doesn't have great soundstage from what I know of it's design, no angled pads or drivers, and from reviews I don't think it has impressions of fantastic soundstage. Don't forget that you want great soundstage if you're gonna be using your headphone for gaming, because it's that property that allows you accurately locate the direction of sounds around you. So really, I think you should try out the AKG K702 that I talked about with you a few days ago....because that has great soundstage, both in my experience of comparing it to my other headphones, and reports on internet....it's my most successful gaming headphone as well as my favourite music listening headphone.....and I know gaming is an important part of your headphone choice so K702 is very relevant.
You asked about closed back & open headphones, what is the difference. It's actually exactly as it's described - closed back headphones the back of the earcup is closed and not open to the air (so solid plastic without holes for instance) - and open back headphones have vent holes or wire mesh on the back of the earcup, so the space behind the headphone driver is open to the environment around you, which is why open backed headphones don't seal off the outside noise as well as closed backs. This changes the way a headphone can perform, and generally closed back headphones can play deep bass all the way down to the 20Hz, whereas open back headphones have the frequency response rolling off steeply somewhere below 100Hz, but this can all be pretty much fixed with EQ by boosting the bass in open backed headphones, with the only problem being that if you boost the bass too much you either run out of amplification power or the headphone will start distorting & the bass will sound loose & flabby for instance. Closed back are better at bass, but open backed headphones normally have better soundstage than closed back, but that's not always the case.