no worries dude
The difference between something like an Asus D2X and onboard audio - is like night and day - you'll notice straight away. Even one of them DG or DX model Asus cards will make a hell of a difference to onboard audio!!
Whereas the difference between an STX and a D2X/DG/DX requires audio geekness abilities lol
The difference between the cards in my opinion does not require audio geekyness.
If you are familiar with a certain scene from a movie or certain passage in a musical piece you should be able to hear difference between the cards or not.
I tend to find that Asus soundcards tend to have a similar certain sonic signature across their range.
I own the DS, D2X and the STX and they all sound the 'same' tonally. I find them on the darker side of neutral to these old ears whereas many people would find them closer to neutral.
To me the difference between the DS, D2X and STX is very very marginal when gaming using a pc orientated gaming headset. For gaming I have the Roccat Kaves. And also like many people I have a dedicated headphone for music use.
On the DS and D2X I found at least in my experience that my dedicated headphones didn't sound any better than my Kaves. If anything it sounded slightly worse. It was only when I re-listened via the STX that the dedicated headphones came into their own.
This is probably due to the headphone amp on the STX as the other two don't have an integrated amp. Also combining with different op amps this could have affected the overall sound.
Musically the STX is subjectively better than the other two cards but then again it should be as it is a more expensive option especially when you consider you require a decent form of output whether speakers or headphones to compliment it.
It all depends on what a person is willing to spend to achieve that result.
Having said that if you were the type of person to go that route and as good as the STX is at least in the pc-orientated soundcard market I am of the impression that it would have trouble against dedicated cd players or dacs slightly above it price point.
An 'audiophille' pc soundcard it might be possibly but it certainly not audiophile overall.
I think Kei would appreciate this that when you start trying to discern which sounds is better overall between a DCS stack system, A Burmester and an EmmLabs that's when you need audiogeekyness and even then it still subjective at best.