I suspect this has to do with much more accurate clocks and anti-jitter technology in the underlying silicon.My experience with my stable of DACs is that the DAC itself is the least important component - anything can b made to sound good, or bad. I agree with the above about timing and jitter, but have a hard time proving it with measurements and sufficient subjective data, but am trying.
Other stuff matters a lot too - power supplies, ground isolation, filters, analog drivers, blah blah. All lots of work too :-(
Its very similar with active devices. People go off on mosfets vs JFETS vs BJTs vs whatever. In general all my designs, using all the above sound more similar than different, unless I f-ed something up.
Another good DAC for the money, BTW is the Allo revolution with the USB bridge and excellent power supply (theirs or yours, been down both roads), if you can deal with their kit-car mentality, documentation (lack), customer service (lack) etc.
I suspect itss why i have finally made my 30-year-old Theta DSpro II sound so good - the clock, USB I/F, SPDIF I/F, power supply, are all mine. And the basic DAC and analog filter were top notch (well there are chip buffers, but very good ones), and there's no magic in either.
G