internal soundcards do not necessarily interfere with the pc. in fact, they have less interference than using onboard and have a quality increase. with that said externals normally have less emi issues since they are outside the case but still since they connect via usb there can be issues if you have usb interference and are still able to be affected by external emi sources. so its not really a win-win situation.. both are about equal in the large picture.
they do make external soundcards as well. things like the creative omni. those accept mic and headphone.
not saying the e10k is a bad choice, its a good piece of hardware. it just is for headphone only so for mic you will need to use an extension cable and go to your pc.