The current pre-release of the client ("pioneer" in the version) is only compatible to itself. So you can only play with other testers. Please be aware!
Xact error, set sound to stereo
See https://forum.faforever.com/topic/796/i-can-t-hear-some-of-the-audio-or-other-sound-issue-what-should-i-do?_=1621533760941