For Vinyl you can press "bypass". For recording your mix you must plug the outputs of the mixer with the inputs of you nottebooksoudcard. I hope you can understand....my english ist not so good
Using RCA-Y-cables (to split the turntables output into U46MK2 and the mixer) is also useful, like that you can switch between line and phono on your mixer.
I think it's comfortable and you have the pure vinyl sound without having it to route through the soundcard.