Incidentally,I recently bought a USB mixer,under the assumption that it was a standard audio interface.The fact that it didn't have a built in sound card,wasn't terribly surprising & I took a haphazard chance in using it as one.
The real issue with it,is that it is only USB1 and that's shocking to me,as I thought USB2 was the standard..especially under the Mackie name.
As it turned out,the mixer's only purpose,was for streaming audio in a live set up,via a laptop and apparently...USB1 is sufficient for such applications.
Even if the mixer was USB2...I wasn't thrilled with downgrading to my PC's factory sound card anyhow.
-Thom