Topic: Really dumb question re headphones
Please excuse my ignorance -- I'm not an audio guy and I'm just doing a podcast. Upgraded my MOTU Traveler to the UCX. Connected my cables from a Grace pre and a Telos One digital hybrid phone tap. Using firewire to a 2012 Mac Pro hex core. Recording to Apple's Sound Track Pro (I know it's essentially deprecated -- I've been using it for six years but I'll switch to Adobe Audition or another DAW sometime soon.) I'm also using, btw, a Neumann U-87.
Input 1 is my mic. Input 2 is the phone mix, set to r100. So far so good. STP sees the feed and will record it properly. (Subjectively, btw, sound quality is much higher than with the MOTU unit.) My problem is, for the life of me, I can't figure out how to send the mix to the headphones!? I know it's certainly very simple, and obvious, but I can't get it. I even called the store, Guitar Center, that sold me the UCX and they couldn't tell me either, even after we went through various settings in TotalMix FX.
With the MOTU Traveler the headphone jack was simply preset so was never an issue. With TotalMix I've tried every combination I could see in the Control Room, but never even got a blip on the meters. Please tell me, in simple terms, how to get my phones to work. I've got to hear my guests to be able to ask them questions 
Btw, I may be an American audio ignoramus -- I sure am! -- but my podcast has made it into the top ten finalists in the political category at the Annual Podcast Awards competition each year for the past five years, in the company of some very high quality (and much larger audience) competition. So I know I'm doing something right even though my audio engineering skills are very limited.