Digital is digital more or less. If you exceed digital zero, the highest level that the A/D/A converters can handle, you will get distortion. You don't NEED a volume fader going to the next stage when transfering in digital, just adjust the output level of the first device to keep it in check.
Be aware that ANY volume change in digital produces extended word bit length. On 16 bit converters, this is hell because it has no way of "averaging" the added word depth. So, putting another device in line to turn the volume down would destroy the integrity of the bit length at the output of the one device. Just remember that with digital mixers, software, etc..., the less processing you do helps keep the fidelity much higher. The more processing you do in digital devices, the more "derived" from the original word bit length you get, which means edgy sound, and more grainyness on lower passages.
Ed