The latest post I just read said that the difference between an R2R DAC and a Delta-Signal DAC is "night and day" and no blind testing is necessary because of that. Soon as someone says that no blind testing is necessary, alarm bells go off in in my head.
The only thing that didn't make me discredit this completely was that the person said the R2R DAC sounded different and it was up to the individual person to decide if it sounded better. But of course, no one is going to be able to do this because most people don't have a $2300 Schiit YGGDRASIL lying around for the testing.
There is one review on YouTube where someone ABs a Schiit BiFrost Multi-bit and says he can't hear a difference between that and a regular 1-bit delta-signal DAC. I believe the BiFrost is a multi-bit delta-signal DAC, and not R2R. (Wow, I almost sound like I know what I am talking about!) But when someome ABs (not blind) the two DACs and says they sound the same, then I don't have a lot of hope of personally hearing a difference between the two with my non-placebophile ears.
I would like to thank everyone for the great input on this thread. I understand way more than I did before about this.
I lived happily with a schiit bitfrost ("uber" model, non-multibit) for a number of years, then purchased the multi-bit upgrade for that unit. I found a noticeable/audible improvement to the sound. It is hard to quantify, but all my music sounded better: more clear, less harsh, better detail. Given that I had liked the huge improvement of my original bitfrost (over cd and dvd player internal dacs), I was worried the multi-bit upgrade would be unnoticeable, but that was not the case. It was a very satisfactory upgrade.