Volumio 3 digital inputs

The new premium tier claims analog and digital input support.
Does that mean that I can connect my pc with an USB A to USB A cable to my pi that connects to my DAC with my hifiberry digi board?
Similar to a digital interface (DDC)?
Or do I need another board with spdif inputs?
Will all of this work lag free?

You need a card with inputs (digital or analog), and then you will be able to select it as a source in the UI.