Neither of them have particularly good DACs. It's the higher end model in each series that has the good DAC (X-Fi Titanium HD, Sound Blaster ZxR).
But what you can do is get an external DAC (NOT a USB model), and then run the Digital output from your current X-Fi to the external DAC. You would get great game processing AND great music output.
I have always run my Titanium HD at 100% Volume when playing music. When I first got it, I did extensive back and forth comparisons with my EMU 0404. Both the EMU 0404 and the Titanium HD had identical output levels during testing, with both at 100% volume. If 100% was +16dB on the Titanium HD, I don't think that would be the case as that would represent a fairly substantial difference in output.
I'm currently using an X-Fi Titanium HD. I like it, but I'd also like something cheap that lets me get back into tube swapping. I was looking at the Aune T1, and that is about the price range I'm looking at, but I was disappointed that USB is the only input for the DAC. Ideally, I'd like to continue using my X-Fi Titanium HD and simply run the digital output from that card to whatever DAC I get.
It's fully possible to have 7.1 surround sound via headphones.
Headphones only have two speakers; you also only have two ears. It is the way in which the audio is presented to your ears that creates the illusion of surround.
The ZxR is a fantastic card for music playback, with a very high quality DAC.
You might also keep an eye out for the X-Fi Titanium HD. It's the immediate predecessor to the ZxR but uses essentially an identical DAC.
I have a pair of DT990-Pro 250ohm headphones. I love them but it feels like I'm running them right on the edge of their capabilities. I often have to turn the volume down to avoid over-excursion of the headphone drivers. I use a Yamaha C-80 Stereo Preamp from 1984 as a headphone amp and it has a VERY powerful headphone amplifier, such that all of my little-dot units were almost immediately retired when I got it. Now my C-80 works these DT990's like a $5 whore.
No one is talking about preventing them from selling anything. That doesn't mean a consumer who wants to make an educated purchase has to spend $140 for a different color of plastic on the outside of the headphones either. Aesthetics is a good reason, but is it a $140 reason? I personally prefer the industrial look of the Pro versions.