responded in your other thread on the hd598. (they really should be combined into one thread if you arent sure what you want to do).
first thing: best advantage on fps games is wide soundstage, good positional accuracy and very little bass output. this is why cans like the ad500x are so good. why lack of bass? bass covers footsteps and most gunshots are treble and mids territory.
can you play games competitively even if you have more bass? yes. skill trumps any advantage you may have here. its still suggested to have decent soundstaging and positional accuracy but you can certainly game well on equipment that is not considered ideal by the masses. my suggestion is to always use what you like the sound of over any advantage it brings.
dt990 is a great open can. bright detailed highs and decent low end considering its an open can. mids are recessed. very vibrant and detailed but at the same time this can be a bit fatiguing for some. the dt880 is more of a neutral version with not as much bass and not as much of a treble edge. still bassier than the hd598 though.
if you wanted even more bass, the dt770 closed can delivers (80 ohm is the bassiest of the three). while certainly not as ideal, they can be used for gaming and for gamers who want bass i suggest them.
a good amplifier for the dt990/880 would be the schiit magni 2. you could get away with something lesser but you may not be able to get the most from your headphones in all situations. if you wanted virtual surround you could use onboard processing on your motherboard if it has it, razer virtual surround or just use a soundcard like the xonar dx which doesnt have much of an amplifier (its dac is the one in the $250 stx).
if you dont care about virtual surround, you could always use an external dac+amp (schiit modi+magni stack for example) or combined dac/amp (audioengine d1, fiioi e10k).