Sure. Cause you can't, really.
No, there is not. That's all in your head, I regret. And I'm not talking about the Singxer Vs RME headamp, where there's logical explanation why you hear differences. A S/PDIF interface can't change the sound of a good DAC. Otherwise, it's a bad interface.
Nope... let's not do that. Seems like you don't really understand the way this place (ASR) works. This is not a forum suitable for arguing opinions about imaginary differences being existant or not. If these differences are there, they have a technical explanation for it (meaning : we can measure it). And I'm not talking about subjective preferences regarding headphones or speakers.
Again : There's no audible difference between USB-In and S/PDIF Inputs of the ADI-2 DAC with whatever S/PDIF interface you would put behind it. Sorry if I haven't made myself clear until now : that's not a debate, but a fact.
Now, you must be joking.