Originally Posted by NomNomNom
Would it be a large noticeable improvement or just a subtle one?
Upgrading from onboard to a decent dedicated soundcard can show a noticeable improvement though it may not knock your socks off. As the other poster mentioned it depends on the source so unless you listen to a lot of high quality audio/FLAC you may not notice much of an improvement.
That said when you start to hear the improvments that high end audio can make you will not go back, since upgrading my soundcard I have invested in a pair of AKG 701 headphones, also had to buy a dedicated headphone amp as they are very hard to drive (power) but boy the difference to me is night and day.
I am awaiting delivery of the amp in my sig (Audinst HUD-MX1) as my other one bit the dust and I cannot wait, I am currently using my cheap AKG K514 headphones in the meantime as listening to my 701's without an amp really does not do them justice, and these K514's even though rated very good for budget headphones sound like absolute sh it, I am only putting up with them as they don't require anything extra to drive them and I can listen to my music at a good volume which I can't do with the 701's without the amp, otherwise I wouldn't be considering them and haven't used them for anything since I got the 701's.
Sorry for the rambling, I guess TL;DR is upgrading your audio equipment can be an expensive business though once you hear music through a very good set of headphones or speakers then you will not go back to cheap, EVER.