You need to install Content Browser then set the Share–>’Open With’ action to ‘Content Browser Exporter’.
Our export plugin simply takes the multichannel QT file and wraps it as an .mxf. Getting multitrack QTs out of FCP X is a bit of a process, however. You need to create new audio roles for each track, then assign those roles to the audio tracks, then map them to output tracks in the Export dialog. XDCAM 50 Mb/HD422 exports must have 8 channels of 24 bit audio. EX export (35 Mb .mp4-wrapped XDCAM) is regrettably not working at present as it is all but impossible to get 16 bit audio out of FCP X (even if you run it through Compressor the channel structure is incorrect). I am working on getting this fixed.