I mean that it is impossible to isolate the effect of the so called 'op-amp burn-in' because the other parts of the UHA 6S burn in as well whenever you use the device so the sound of the whole thing change. You won't know which change and how those changes interplay.
One can get another brand new pair of op-amps (same model and batch) and compare how different does it sound as compared to the used one. That will be to try to isolate the effect of 'op-amp burn-in' =)
Haha no. I have just received the Clip+ and the IC so I was letting both run in together with the UHA6SII when I was taking that photo. I bought the Clip+ for fun only ;)
For comparison, I will solely be using direct USB out from my Macbook Pro versus USB --> U3 --> Coax to see how the USB receiver on the UHA6SII fares against its SPDIF input, holding the source constant (which is my Macbook Pro).