There aren’t any specific audio settings for the server and Plexweb is very limited as a ‘Player’, so no need to go crazy with settings.
If you want more ‘granularity’ for audio settings - or a better chance for Direct Play - use Plex Media Player (best) or The New Plex Player (unknown):
https://www.plex.tv/media-server-downloads/?_ga=2.115603270.1993529163.1575302888-1864473727.1455657109#plex-app
(the link is misleading - The Player App is actually there under it’s tab - and you should go right to it)
