I wanted to start a thread so others can learn fro my experience. I also didn't want to keep hijacking a previous thread I started to post in. I will update this as things progress.

The new MacBook Pros are out. I needed something new to replace my late 2008 MBP dinosaur. The new machines feature an OLED screen where the functions keys used to be. They also only have 4 Thunderbolt 3/USB-C ports. They come with the latest version of MacOs Sierra 10.12. I'm having an issue getting tracks to even start playing.

I'm running Serato DJ 1.9.4. My mixer is an Allen & Heath Xone:DB4. As of 1.9.3 SDJ is compatible with MacOs Sierra. But this page says my mixer is not supported on Sierra.
support.serato.com

But if you follow the links to the A&H drivers page you will find the 3.3.11driver adds support for Sierra as of October 2016.

I can play audio just fine through the mixer from the OS (like from iTunes) and the MIDI utility confirms that MIDI data is getting through.

With the mixer disconnected Serato will play tracks in the offline mode. As soon as it detects the mixer being plugged in the track will stop and cannot be started again. When the mixer is plugged in SDJ does say "Connected to Allen & Heath Xone:DB4" I can use my hardware decks to scroll through the library and assign a track to the deck. The play/pause buttons start flashing. That's as far as I can get.

I opened a ticket with support and they came back with the "your mixer isn't not supported by Sierra. Downgrade your OS or call Apple" response I expected. I'm pretty sure that's never going to work. For the sake of science I was going to upgrade my 2008 MBP to Sierra to rule out the OS being an issue but El Capitan 10.11 is the newest version support on that hardware.

Is there any diagnostic info I can get that can expose the cause of the issue?