“So what do those much more expensive DACS do for sound?”
Distort the sound less. Have way better output stages than the lower cost units. Generally speaking of course.
How much does a DAC do the more expensive it is?
Having spun an Oppo 105 for many years on its own before adding a Schiit Gungnir (bought for a generous steal from a wonderful seller here), I was immediately struck with how much more presence and detail the Schiit added to the Oppo's presentation.
That Gungnir, even new, pales in comparison pricewise with 4 and 5 figure DACs I see for sale here.
So what do those much more expensive DACS do for sound? I mean, how much more information can be dug out of the digital files? Is it akin to what a good phono stage can do for a cartridge?