Who hasn't heard differences between bit-perfect digital audio sources, software running on it, and digital audio interlinks connecting to it.
The reason for this is that the digital audio source generates interference that cannot be fully blocked in the DAC. Therefore it would be best to have a clean digital audio source.
For the cleanest digital audio source we created the UPL series, a simple battery powered player that plays WAV files from a USB stick.
The digital audio interface can also create ground loops that feed even more interference into the DAC.
We use optical Toslink interface that does not have this problem as it offers perfect galvanic insulation with zero stray capacitance.