USB audio Codec should be the right choice according the turntable's User's Manual and from personal experience with USB audio devices. (I have one USB headset that comes through the USB audio Codec and another that shows up as a specific named device — I am not sure what makes the difference.)

With USB audio Codec selected in System Preferences âž­ Sound âž­ Input there should be an input volume slider and an input level indicator below the list of input devices. Play a record on the turntable and slide the input volume slider to the right until you see input reflected in the input level indicator. Usually you would want the input level should peak somewhere between the mid point and maximum on the far right.

Give that a try and see if you are receiving an audio signal through the USB audio Codec or not.

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein