High resolution digital is dead. The best DAC's killed it.

Agree. The Redbook standard was likely sufficient all along. Just needed a good DAC to properly decode it. Low-jitter transports also contributed to this realization. 

Yes for me it is low jitter, better differential linearity and less noise with 6 bit sigma delta DACs that are the reason for recent improvements in sound.

Upsampling helps randomize differential non-linearity.

As usual, noise is always assumed to be random and if high enough it can be all filtered out. The reality is that it is rarely perfectly random. Just like jitter, if it was simply all random then it would never have been a problem to begin with.

R2R has its merits as a technology but is limited in resolution due to differential non-linearity. 6 bit delta sigma DACs are kind of hybrid between old single bit sigma delta and R2R.

That said DSD is still a highly elegant approach especially at 4x or higher, as it inherently has great linearity and then noise is pushed way up and far out of the way.

It seems that DAC chips do suffer from everything being crammed together on a chip. So discrete DACs like PS Audio DS and others seem to have a more analog sound even if their measured performance is not as impressive as the latest Sabre based DAC.

Lots of ways to skin a c@t!

I don't know if there is an affordable 24bit R2R DAC yet.

Affordable is of course different for everyone but my MHDT Lab Pagoda (PCM1704) sells for about $1300 and does 24/192 natively. Sounds wonderful.

 The simple answer great streaming it is a product like blue sound. By the time you try to work this out the kinks with a computer you could afford a blue sound Node 2

The vast majority of my music is 16/44.1 and my focus has always been to get the most out of the format. The first DAC which proved to me 16/44.1 was "good enough" was the dB Audio Labs Tranquility. According to many the DAC, with it's cheap TDA1543 chip and lousy measurements, couldn't possibly sound good. Apparently dB Audio Labs subscribes to the "everything matters" philosophy of DAC design and proved the naysayers wrong. I still own and use the Tranquility. 

A few years ago I decided to explore the high-res world for myself and purchased enough good sounding music to care about hearing it at the native rate. A couple of DACs later and I finally settled on the MHDT Lab Pagoda. This DAC sounds fabulous not only with 16/44.1 but higher rates also. Funny though, I have little interest in high-res at this point. Good old Redbook is all I require.