No sound thru USB device on playback

Just starting using Audacity 2.4.2 with M-Audio “Air” USB device. Pair of stereo mics into device, to iMac via USB. Headphones plugged into device and they are working on recording. Problem is no sound thru phones on playback. In Audacity Preferences: I have selected Core Audio (only choice and instructions indicate correct for Mac) and I have selected AIR 192 6 for recording, 2 (Stereo) Recording and likewise for Speaker I have selected AIR 192 6. In my System Preferences I have selected under Sound>Output AIR 192 6 type USB.

When I switch this setting in System Prefs to Internal Speakers Built-In I do get playback sound thru computer speakers. So maybe this is an M-Audio question & not an Audacity topic? But I’m hoping someone else has encountered and solved this problem. Thanks, Don

Does playback through the M-Audio work with other applications (such as iTunes)?