Apple has just released macOS 10.12 Sierra that has a regression that breaks Direct Mode.
- Until they fix it, or I find a user friendly workaround, you have to disable Direct Mode (option in Audio System page of preferences) to get playback to start. In Audirvana Plus 2.5.4, it is disabled by default.
- If you are Terminal-savvy, there is a way to get it back: you can replace the faulty kernel extension of 10.12, IOAudioFamily.kext, located in /System/Library/Extensions, by the one from El Capitan 10.11.6, if you have a backup. You may need to disable SIP during this replacement operation.
Other than this Apple regression that breaks Direct Mode, Audirvana Plus 2.5.4 is fully compatible with macOS 10.12 Sierra.