Not sure if this also applies to streamers but might help explain why sound quality is suppose to be better with usb. I always heard that usb was the preferred input for dac’s. It’s the one that’s recommended for my dac.
So there is a lot of misunderstanding surrounding digital audio. With the 'bits are bits' argument often being used.
It's true in the sense that the actual CONTENT of the signal, the audio data itself, the 1's and 0's will either reach the DAC intact, or they will not.
There are no 'audiophile bits' and as far as data integrity goes, optical SPDIF, coaxial SPDIF, AES, USB, I2S or anything else will be able to get the exact same data to the DAC.
BUT, the issue with audio is that it is not purely about data integrity. TIMING is important too. If you have exactly the same audio content, (ie: Exactly the same PCM samples) but they are converted at different times, you'll get distortion.
This is called jitter.
USB is an 'asynchronous' protocol.
This means that the timing is actually controlled by the DAC.
A super simplified explanation is that audio data from your or PC is sent to your DAC, often in chunks at a time.
This is put into a buffer on the USB receiver of the DAC, and then the DAC uses its own internal clock (crystal oscillator) to determine when to convert these samples.
When the buffer is getting low the DAC instructs the PC to hand it some more data and it sends more to put into the buffer ready for conversion.
The DAC is dependent on its own clocks for timing accuracy, and whether you plug this DAC into a Mac, a PC, a Pi, or any other device, the jitter performance will be absolutely the same. The timing with which the source device sends data to the DAC makes absolutely no difference so long as the DAC always has the next sample in the buffer ready to convert.
SPDIF is a 'synchronous' protocol. And unlike USB, the source you use DOES have a direct impact on the quality of the output of the DAC, even if the data itself is completely identical.
Why? Because with SPDIF, the clock signal is actually sent by the source device (PC), NOT the DAC's own clocks.
Data is sent in a constant stream, accompanied by the clock signal, and so if there is additional jitter on that given clock signal, the DAC itself will be converting samples with less accurate timing and the analog output will be less accurate.