No extensive tests this time, just some thoughts and findings instead. Incrementally, of course.
First case, how to make sure that the analog inputs are not digitized? Any ideas?
Let's make some tests. I connected output of the signal generator to the scope and to the input of WiiM Amp first. Its outputs are connected to the differential scope. Result is below:

We can see how the AD/DA conversion affects the square wave. We can also see the time shift which may indicate the delay in the processing.
Now the Vibelink Amp.

This time there is almost no delay. And no sign of the conversion affecting the wave, except the overshoot of the amp.
First case, how to make sure that the analog inputs are not digitized? Any ideas?
Let's make some tests. I connected output of the signal generator to the scope and to the input of WiiM Amp first. Its outputs are connected to the differential scope. Result is below:

We can see how the AD/DA conversion affects the square wave. We can also see the time shift which may indicate the delay in the processing.
Now the Vibelink Amp.

This time there is almost no delay. And no sign of the conversion affecting the wave, except the overshoot of the amp.
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