There are none. Plex for Windows does not support audio passthrough.
Use Plex Media Player, PMP, instead. It is targeted towards home theater users. Download from the announcement thread.
To configure audio passthrough, you’ll need to put PMP into “TV Mode.”
Click on the TV icon in the upper right.
Then click on your username and choose Settings → Audio
Set device type, number of channels, passthrough, etc according to your setup.
Links to additional documentation below.
