For a pair of cans the sound is the most important bit. In this department X2 Aurel performs well enough, considerably better than what you'd expect for its price-range. The headset is somewhat neutral with a slight emphasis on the bass. Since there are very few gaming headset to actually go for a more neutral response, instead of an over-emphasised bass, this is a pleasant turnover, to say the least.
There are some misses though. The bass is not as tight as I would have liked it, and it does feel somewhat boomy. The treble also is extended, sharp and turns fatiguing, especially after a few hours of use. Compared to HyperX Cloud, it lacks a lot of detail and the bass is not as controlled, but then again the pair is also almost half the price.
I have used these headphones for about 2 weeks, with at least 50 hours of burn-in. I did not notice any kind of change in terms of audio, so what would you'd get out of the box is what you'd get later down the line.
The slightly warm bass lacks some tightness and speed, and doesn't manage to keep up with faster tracks like Hajnal or Dream Theater's Scarred. It also feels slightly boomy, and that might detract from the experience. Thankfully, though it's slightly emphasised, it doesn't sound overpowering.
The bass transitions nicely into mids, which are balanced and pleasant to listen to. There seems to be a slight emphasis towards the upper-mid / lower treble, though nothing too bright or poignant. It just adds a bit more vocal presence, which is almost always a plus.
The extended treble is also clear, but bright, and it becomes fatiguing after a few hours of listening, especially to let's say, metal tracks. The cymbals lack the splashyness I would have liked to hear, and are at times, out-paced by HyperX Cloud, or ASUS' Echelon.
Stereo Imaging is actually quite pleasant, though not perfectly refined. It's a bit better than the HyperX Cloud, though the sound-stage is actually worse. The headset doesn't have a very wide or deep soundstage. Sound tends to sit either to the right, or the left, and almost always at the same distance, close.
This is also sad for positional audio, since this is, after all, a gaming headset.
After a few hours of Battlefield 4 & Counter Strike, I came to the conclusion that the narrow sound-stage hampers positional sound in a 3D environment. Even when I used Dolby Home Theater (as bundled with ASUS RoG Phoebus), there was little improvement.
Outside of the competitive gaming territory, where distance and position actually matters, the headset stands quite well. Games like StarCraft II, or Divinity Original Sin, where multiple sounds compete for "listening time", get along well with Aurel, even though a bit more detail would have been grand.
The small included in-line microphone is adequately positioned close to the mouth, and the audio is quite decent. Since most in-line mics or average at best, in the rest of cases, having a decent one is a great thing. The microphone picks up the voice naturally, though it also picks up more environmental noise than say CloudX's mic or , or even the smartphone mic. Other than that, I was fairly surprised of its quality.