How about subjective proof? In the form of the designer of the DAC in question preferring Unison to coax?No objection from my side. Unison is a noise filtered usb input, needed for usb sources but not superior to a coax source. If so, I would like to see objective proof.
Also weren't you part of a really long discussion thread where @ArmchairPhilosopher explained how with spdif there's no way to recover from certain errors/dropped packets, as opposed to Unison where it is possible? Could've been somebody else.
There's also an old Stereophile interview where Mike M talks about how you can actually shift things around in the soundstage by moving the optical cable that's transmitting the digital audio.