According to your Volumio device you can have ANALOG or DIGITAL OUTPUTS as audio output choices.
USB DAC: Attach an USB DAC (2.0 USB and up) using a high quality USB cable.
Suggested in particular for Tidal MQA hardware decoding and DSD native playback. Samplerate supported until 768KHz/32bit PCM.
USB DAC 5V low-noise filter [Volumio Rivo]: Dedicated port for a better clean digital audio signal, without power noise disturbances.
SPDIF [Volumio Primo and Volumio Rivo]: Attach a COAX digital DAC or Audio receiver. Samplerate supported until 192KHz/24bit PCM
ANALOG RCA [Volumio Primo]: Using the internal Primo’s DAC D/A converter go out from RCA OUTPUT and go in to the AMP/PRE AMP
I2S DAC/HAT: Connecting an I2S DAC/HAT to the compatible SBC board you will expand the audio outputs according to the I2S device connected. A long list of I2S drivers compatible inside PLAYBACK OPTION→I2S MENU
AES/EBU [Volumio Rivo]: Attach a digital balanced XLR cable. Samplerate supported until 192KHz/24bit PCM