I'm a FCP and Compressor veteran making the switch to Adobe. I have a client asking me to deliver their video as M4V and M4A files. I was able to create an M4V by Exporting as MPEG4 and dropping the Multiplexer (muxing).
Just disable the video option. M4V is a MPEG-4 file with both audio and video. M4A is a MPEG-4 file with only audio, no video. So in your AME settings just uncheck the export video box and you're good to go.