I can hear playback by connecting my headphones to the "main out" channel, but not when the headphones are connected to headphone channel one or two.
I am using Logic Pro X version 10.2.0 on a Mac OS X El Capitan 10.11.1.
I am using the Studio 192 192kHz/24 bit, 26x32 USB 3.0
The answer is probably simple, but there is not much information on this.