If an audio driver appears in the Reason preferences Audio tab with a red cross next to it, chances are that this driver is already in use by another application that cannot share the driver with Reason. Quit that application or check if there is a Run in Background option in the preferences for this other application and activate this.

A red cross can also appear if there are duplicates of a audio driver, like e.g. if You have managed to install several of the Apple Sound Manager driver, which can happen if You haven't been aware of language versions etc. Do a system wide search for the audio drivers name (or something similar so You can see all the possible iterations in the search result) and delete the oldest driver of the duplicates. Restart the computer after this and try again.