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.