I am using a Mac Mini core with a retina Macbook as one of its remotes. My problem it that it is not possible to play to the local outputs of the Macbook. In Audio Settings under “Connected to this Mac” the outputs of the core are listed instead of the local ones (see first image). Completely removing and reinstalling Roon from the Macbook does not solve the problem.
The second screenshot is from my Macbook Pro connected to the same core and shows how it should be - a list of local outputs followed by those of the core.