Oppo 205 and external DAC?

I use my Oppo 203 as a transport, and it is connected to a RME-ADI2 DAC via coax.  The ADI-2 then runs balanced to my pre.  There is a subtle, but noticeable increase in detail when using the external dac versus the internal in the Oppo.  AFAIK, the internal dac in the 205 is better than what's in the 203, so there may not be much improvement with the 205 going to an external DAC.  

hi 
But I am not getting sound from the coaxial output when I stream music from mac air to oppo ( by usb ) then from oppo to dac?

Any ideal?

Is there a S/PDIF output setting in your 205 that turns on / off coax output?  Likewise, is there a setting in your DAC to set the input to coax?  I have to set my DAC's input to coax when using the Oppo as transport, otherwise there is no sound.