I agree with Onhwy61 - for instance...
I bought a Bifrost DAC with the USB port to stream from my iMac.
In order to mitigate the obvious USB related issues, I tried a couple of USB cables and settled on a double cable that is joined at the DAC
- one cable was for power the other for signal
Even though this worked extremely well, I then decided to try a v-link192 USB-SPDIF converter connected to the DAC via an RCA SPDIF
It was quite clear the USB interface on the Bifrost was inferior to the USB interface on V-link192.
However, the SPDIF input on the DAC appeared to be as capable as the SPDIF output on the V-link192.
The resolution improved dramatically.
My guess is the USB "interface" selected for the Bifrost had more to do with its very sffordable price point
So, I am assuming that between two connected components, similar cost saving measures that may have been applied during their manufacture, may result in similar inconsistent results between their individual digital inputs.
Basically - its a craps-shoot - simply because, the actual circuitry within a components digital interface may offer a different level of performance compared to the component it connects to.
Quite often, the actual "Interface Specification" only identifies a minimum level of performance in order to work.
Regards...