I'm having the issue with no sound coming out of my Mac through the FM3 also. I have the FM3 connected straight into my MacBook Pro via USB. I don't have the headphone version of the FM3 so I'm using a Y cable out of Output 2 into a headphone amp. I have sound out from the FM3 when I'm playing guitar through it. I have Output 1 copied to Output 2. When I play a YouTube video the Analog Out and USB In meters are in fact lighting up but no sound. (on the Mac, FM3 is selected as the In/Out device) Any ideas?