Is it possible to put a link to music into the text of a post? Specifically, I would like players to be able to listen to a song I host (offsite) as "mood music." I would prefer not force them to download the music, or just link to YouTube or whatever (although if I have to, I guess that will do in a pinch). Basically, I'd like them to be able to hit "play" and listen while reading and replying to a message.

No.

The best you can do is provide a link to the file or page where it's hosted that they can open in a separate browser window.

How it's handled then is dependent on the device and browser they're using.

Thank you.