Just purchased a POD HD desktop. USB plugged into my imac. Headphones plugged and guitar plugged into my POD. Can record and playback with logic pro..headphones pick up as output just fine. Problem is when I want to use the POD and associated headphones to listen to computer ouput. Nothing happens. I go to preferences->line6 devices->audio MIDI setup and select the POD HD as the "sound output" but there is no sound..when I select the "Built-in Output" I get my sounds. I had a POD XT that worked just fine. the POD HD does not seem to work..I'm sure its a user error..can someone offer some guidnece?