The 3.5mm plug goes straight into my 2014 MacBook Pro Retina headphone/mic jack (the MBP has one jack that passes both signals). I didn't need to plug the USB in. I didn't use the inline amp. Wasn't necessary for the audio I need. In fact it didn't work just by plugging in the USB. The mic and headset sound just fine plugged straight into the MBP's headphone/mic jack.