You cannot comect those powered monitors to the Onkyo.
There is no room there for the Onkyo 7.1 system. It is superfluous and should be looked upon as a standalone system.
You could probably connect the mac to the dac, and the dac to either the powered speakers or the Onkyo system.
Gut, with "Y" connectors on the output of the DAC, you could peobably connect the DAC to both the Onkyo (aux input) and the powered speakers..