the only difference between this and an internal add-in sound card is that this is external, away from all the electronic RF interference that can go on in a PC case.
it has a dedicated sound processor, just like an PCIe card, but it rides the USB bus. the onboard ASrock has a sound processor but it requires the CPU and RAM to do the lifting, while not a problem for the CPU nowadays, they are not made for audio and cannot do it as well as a dedicated audio processor can. the omni is and does.
as for internal add-in cards
http://www.newegg.com/Product/Product.aspx?Item=9SIA24G2KG1917
http://www.newegg.com/Product/Product.aspx?Item=9SIA24G37P8676
these are 2 Audigy cards, I have personally used the 5.1 audigy card and it is great.
the 7.1 card has 2 more channels and gold plated plugs everything else is the same, more or less.
I have been a Creative User for ever it seems.