This does not make any sense. If you want to use the DAC, then by definition, you will be running 2-channel, not Dolby Digital.
What you do is set your sources, either the Blu-Ray player, the Smart TV or the cable-box to 2-channel PCM output.
Then you drive this digital output to the DAC. Then you connect the DAC analog outputs, L and R to the SS processor. Then you get 2-channel from the processor and your speakers.
If you do this, I would highly recommend adding a reclocker to cable from the digital sources. They will have much higher jitter than a CD transport.
If you want Dolby Digital and surround-sound, then your DAC will not work. You will need a good SS processor instead.