Okay.
Well, the first thing to say is that is isn't Audition...Audition simply doesn't do signal routing. It records what it's been given by a sound device, be that the built in sound card on your computer, an external sound card...or your Behringer.
I've just downloaded and read the manual for the Q502USB and I may have spoken too soon when I said the Q series fixed the USB return problem. The manual isn't totally clear but it implies that, when the "USB/2TRK to monitor" button is pushed it may cut off the monitoring from the mixer inputs. Is that what's happening when you say that this selection cuts off audio from your headphones or does it ALL disappear? If it's only the input monitoring that disappears then it may be a stupid design decision at Behringer.
If it ALL disappears then make sure you have the latest drivers from Behringer downloaded from here: BEHRINGER: U-Control-Downloads
Also, check the Windows audio control panel and make sure the Behringer has been detected in both the Record and Playback windows.
Then go to Edit/Preferences/Audio Hardware menu in Audition and make sure you have ASIO set as the device type and the Behringer mixer selected in the "Device" box.
If it's only the INPUT (i.e. Mic) signal that's disappearing then there may be a work round for you. Select the "USB to Cntrl Room" setting but, within Audition select the little "I" box at the left hand end of the track you're recording in multitrack. This will feed the signal you're recording back down the USB without recording the existing music in the new track. Be warned though that you mic will be doing a round trip via your computer and latency (delay) may become an issue. You can play with the I/O Buffer size to try and make this latency as low as possible without getting recording dropouts.
I have to say--and you won't like this--that the small Behringer mixers tend to be a bad choice for audio interface. They have lots of shiny (but useless) knobs but fall down on the basic tasks of routing your signals in and out of a computer. Even the most basic simple standard audio interface tends to have an effective form of "direct hardware monitoring" and usually better quality pre amps as well. I contribute to a couple of recording forums and problems with signal routing on Behringer mixers are probably about the number one question (and not just Audition...on every major computer audio package). Something to consider for the future.
