First I select the Line 6 Asio for Amplifi in the audio interface. Then I openthe mixer panel and clicking on each channel you can assign what you want to put on that channel. In my case I can choose between Amplifi stereo R/L, Amplifi Left, or Amplifi Right. I'm not sure what these options mean, because whatever I select nothing changes in term of sound. But anyway, when I select one of these, then FL studio feels my guitar when I play and I can also start recording. But at the same time, when I select one of these option (it doesn't matter which), the sound get weird.