Ardour/Mixbus woes

[Michael Zacherl.]

Hey, 
I'm trying to use Ardour/Mixbus on OS X since Logic doesn't allow sample accurate automation.
(which I need for my current project)

Unfortunately I missed to configure an Aggregate Device which causes troubles when trying to route audio.
Maybe I'm overworked or just blind but I can't find where to change the audio interface settings in Ardour!

Would someone be so kind and point me there? 
I can route a single channel strip via Jack OS X but I don't see the Master.
Nor does it sound.

Thanks a lot, Michael.

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