If you're host is being muted on connection, it's because your friend has been given privileges to connect without needing permission. Right now, we assume that the friend is the only person connecting in that case.
To unmute, just unmute the host machine the same way you would normally do that on Windows.
To make it so this doesn't happen, your guest can open his advanced settings, and add this line:
If this is happening when you're connecting to yourself, and you can't get sound to work through the stream, you should confirm that your sound output is being delivered to the default playback device. Parsec always captures the sound on the default playback device in Windows.