Ive got the same issue. I cannot use halion sonic standalone. There are no options in the audio driver dropdown. I have found this article that would explain whyt it’s greyed out since I have a current version of wavelab e;lements installed.
Still, this does not address why i have no audio output in the standalone halion sonic. Being able to use it standalone and in other hosts was my main reason for upgrading from SE
good luck. I hope this helps