how to reload audio driver

If you deleted a macOS audio driver, then either restore from a backup or reinstall macOS over top of itself.

If you are asking about a third party audio driver, then re-install the audio driver from the same source you used before (better yet, see if there is a newer version available from the developer).

If you reinstalled macOS and are still having the issue, then it is unlikely to be a driver issue since macOS would have reinstalled the original macOS driver. I'm not sure how you are reversing the speaker config, but it sounds more like a corrupt .plist preference file issue or a hardware issue.

Have you tried creating another user account and testing the speakers while logged into the new user account?