Volumio Primo has its DAC onboard. It mounts an ES9028Q2M DAC via I2S connected to the Tinkerboard S mainboard.
This means you can choose between :
RCA ANALOG OUTPUTS (connect RCA cables to the inputs of an amplifier)
COAX SPDIF DIGITAL OUTPUTS (connect COAX cable to the input of a DAC)
You can also choose the USB OUTPUT of Primo as third choice, to connect USB DAC and reach the max PCM audio resolution (768KHz/32bit) and other advantages, such DSD and MQA stream.