Heya - snipped a bit of the post
1st question to you would be PC or console?
Main thing is the sound hardware - after that then you're probably 90% done.. A $30 set of Samson SR850's with the right mixer or soundcard will do you a hell of a lot better than a $800 set of headphones with stereo sound.
For pure soundwhoring the AD700's are pretty much the king (because of how they're lacking in other areas - no pesky bass to drown out where the clicky-clacky footsteps, crunches of gravel underfoot, ting of a grenade pin being pulled, shhht of a sub-machine gun getting reloaded etc are coming from)
However, if when a bomb goes off behind you you want to actually "feel" it (or hear it) then the AD's won't convey that at all. Sort of like playing by braille, but with you ears. You'll know where everything is but there's no colour, just the pointy indications.
Call that MLE's 10 for competitive
Going down? from there you can work out the competitive/fun ratio you want - more colour comes with more distraction. Some of that is from more bass, some from a smaller or narrower or shallower soundstage (the virtual sound sphere the headphones project)
OK - hardware now. Firstly (and most importantly) you need a mixer. This converts game sound into a full surround experience in the stereo headphones. If you're on a console then the mixamp, dss, recon 3d etc on the first page of this thread are what you're after. (mix amp is a mixer, not an amp). If you're on PC then you need to look at Nameless's
thread for a soundcard (starting at around $30).
The mixer/soundcard are what does 90% of the work and once you have that sorted it then comes down to what you want to hear with respect to position, clarity, accuracy, distance etc.
The mixer/soundcard should also look after the voice/mic side of things
You might get a 25/9 kill/death with AD700's vs a 23/11 if you went with the AKG's but what you hear out of the AKG's would probably be far more pleasant to the ears - that's where it's up to you
Now - amps, dacs and all that - not needed at all if you choose the mixer and it works fine with your headphones you choose. The AD's, HD598's, PC360's are all easy to drive headphones (meaning they don't need anything else to sound their best. The AKG's you mentioned improve more with more power (from an extra amp). Don't fret - there is a world full of headphones that don't need an amp, just make sure you find out where yours fall before you buy.
Personally, with what you typed initially (soundwhore extrordinaire) I'd suggest the mixamp and AD700's and you'll be pwning (am tipping you're on console). With that setup you could look for a second set of headphones for when you're not roflstomping noobs and want more colour in your audio.
