"sound interface" isn't actually a correct description. It's kind of like someone that doesn't know much about computers saying " I need more megahertz for my harddrive".
I think the actual name your looking for is "audio interface", not to be confused with "midi interface", although they are both often found together in many "sound cards".
An audio interface is a broad term for different devices that basically do the function of a sound card, which is to record and play back audio. It might be a soundcard, or an external rackmount unit, or a control surface or whatever.
au·di·o ( P ) Pronunciation Key (ôd-)
adj.
Of or relating to humanly audible sound.
Of or relating to the broadcasting or reception of sound.
Of or relating to high-fidelity sound reproduction.
in·ter·face ( P ) Pronunciation Key (ntr-fs)
The point of interaction or communication between a computer and any other entity, such as a printer or human operator.
That's about as long as I could make it.
