I don't have a mac, so can't be much help in that respect, but it would be helpful to know what DAW software you are using.
I did find this regarding Behringer USB mixers.....
"The USB interface built into the mixer is class compliant under Windows and uses core audio driver on a Mac. This means that it doesn't need a driver to be installed when used with Windows XP or Mac OS X.
Ver. 3 Mac OS X
First go to your system preferences > sound > input > select USB Audio CODEC. Output > select USB Audio CODEC. Second, go to applications > utilities > audio midi setup > audio devices > default input > select USB Audio CODEC. Default output: > select USB Audio CODEC. System output: > select USB Audio CODEC. Properties for: > select USB Audio CODEC. In addition, make sure to select 44100.0 Hz and 2ch-16bit for the audio input and audio output.