My wife's iPad lightning to headphone adaptor has no problem driving the DT 770s to moderate SPL and the bass is undistorted; music choice is symphonic metal so the music I listen to isn't shy on the bass.
I had that same sound card. It's ok but the amplification part isn't up to par with a real amp. Nor do I like having a source that is inside the PC. In my experience, the best sound is getting the source and amp out of the PC power supply loop. So an external solution works best. Sure you can use the soundcard as a dac or source but based on what he's describing I would try external powered amplification at least and an external dac and amp for the best sound quality. Positional audio with the sound blaster is essentially a non factor. It really didn't help as much as upgrading the rest of my stereo. Now that I have a clean source and amplification. Plus some fucking good speakers. Directional sound is much improved. I get surround sound out of two speakers.
I got my AD900X finally. They sound really good, I am pleased with that. Only thing is that, despite having a very large head, they are actually somehow too big even for my head. I will try the rubber band mod, but the clamping force seems to mostly be below my ears on my jaw which is not super comfortable. The top of the pads barely touch my head. I'm not sure who has a head large enough for this to fit parallel to your ears. Otherwise, they are quite light and the "wing" things don't bug me, although they also basically do nothing to hold the headphones up on my head. Maybe the rubber band thing will help.
Beyers DT-880 remain my all time favourite comfort wise, with big glasses. Have had extremely long sessions (from waking up to going to bed literally) with them and totally forgot they were even on my head. So light and so soft!
I broke them (by dropping them too many times, after 10 years of service) and am waiting for some help to fix them. In the meantime I am using Philips Fidelio x2hr and they are not as comfy (much tighter) but still actually quite good and I can wear them all day without much trouble as well. I might loosen them a little bit though, since it's quite uncessary to have a tight fit with open headphones. Or find softer pads more like the beyers.