How can I get my headset to work with my MacBook Air? (13-inch, Mid 2013) I would love to use my Sennheiser PC350SE headset with my MacBook Air (13-inch, Mid 2013 model).

I recently purchased a Startech Headset Splitter hoping that this would allow me to use the headphones and microphone together. However the audio continues to play from the Mac, and only the Mac's internal microphone is being detected. I checked the Sound Preferences and found no entry for any external headset or external microphone.

Is it possible to use a headset with my MacBook Air? Microphone quality is important for me as I take part in a lot of online meetings and don't want the sound interference from other participants, system sounds or background music.
You can use the earphone portion of the headset by plugging the appropriate cable into the audio output jack on the Air. The Air does not support plug-in microphones as it only has 1 analog output jack. The boom and Startech splitter will not be of use in this configuration.

My recommendation would be to purchase a Mac-compatible stereo headphone + mic to USB adapter. That would enable you to enjoy both quality audio and benefit from the close-field mic boom on the headset. Alternatively, you can just use the headphone part for listening and the built-in mics for speaking.