I think the issue is getting confused here. 
Yup, comparing the sound of Dacs and or other components in the replay chain may indeed be valid and an analogue and digital replay chain can indeed sound different.
It all gets a bit more complex when you play digitally recorded vinyl. Given, according to some at least, the differences between analogue and digital are obvious then these people should have absolutely no problem identifying a digitally sourced recording on any medium.
This certainly hasn't been a resounding success in my experience.
So, lets not get the source and replay chain mixed up.
Regarding my preconceptions. Of course, I have to accept this may be true but bear in mind it wasn't that long ago I was all Vinyl and viewed digital with the same scepticism as many here.
It was only after sitting down and listening, hopefully with minimum preconceptions, but some will have been present, to a first class digital replay system that I had to finally acknowledge it beat my Vinyl system to a pulp.
Perhaps my Vinyl system wasn't what some would consider first class, but a London Decca Gold with Hadcock 228 built on a custom Thorens TD 160S produced a fairly decent sound against the vast majority of turntables I had heard.
Add to this I decided to sell my entire record collection, record deck which i had spent years modding, my SUT, Pre amp etc etc and start from scratch, I would argue that my preconceptions didn't stop me taking what was at the time some very painful decisions based purely on quality of sound.
Single spur balanced Mains. Self built music server with 3 seperate linear PSU, Intel i5, 16 GB RAM no hard drive (various Linux OS). Benchmark Dac2 HGC, single ended XLR interconnects/Belkin cable. Exposure 21RC Pre, Super 18 Power (recap & modified). Modded World Audio HD83 HP amp. Hand built Monitors with external crossovers , Volt 250 bass & ABR, Scanspeak 13M8621 Mid & Scanspeak D2905/9300 Hi. HD595 & Beyer 880 (600 ohm) cans.
The whole problem with the world is that fools and fanatics are always so certain of themselves, and wiser people so full of doubts.
-Bertrand Russel
John.