The sad truth is there is no checksum process for digital audio signals AFAIK (as opposed to data signals sent over e.g. USB which do have error checking and retransmission in the protocol), so it is quite possible that what arrives at the DAC input is not bit perfect. It would be very helpful if one of the test sites could do that comparison (original signal vs delivered signal) and report how much, if at all, is lost due to small errors in forming the digital pulses that might be causing losses. That way the industry would at least know, or eliminate, one source of worry concerning the quality of the digital signal.
We are still talking about a digital signal when it arrives at the DAC input. While all signals are 'analog' what this means is that the received signal only has to be clear enough to distinguish zeroes from ones reliably. Whereas with an audio signal in analog form, the equipment is tracing every detail of the sound on a base carrier signal. In the latter case, generating the base carrier signal smoothly and with plenty of power reserve makes a huge difference. Which is why most power amplifiers are mostly sophisticated power supplies with modulation circuits sitting on top.*
I cannot say I have heard any noticeable difference between sources once noise, cabling and generating software (e.g. Roon) are correctly addressed, so I am struggling to justify further expenditure upstream. But that is only my experience, based largely on auditions at high-end dealers. Very willing to hear contrary views from others here who actually own and live with better upstream equipment.
*I recall a celebrated Australian power amp designer, Peter Stein, once saying "it is like trying to paint a masterpiece with one hand while someone is shaking your other hand vigorously"
