Schiit Yggdrasil -- 21 bit?


Schiit says that Yggdrasil is a 21 bit DAC. But the DAC chips that they put in the device ( Analog Devices AD5791BRUZ, 2 per channel) are 20 bit with the error of plus-minus 0.5 LSB.

How can the DAC be 21 bit if the chips are 20 bit? Using two chips per channel does reduce the RMS voltage of the noise by  a square root of 2. But how can you get to 21 bit from there?

Can someone please explain.
defiantboomerang
I have read that most properly designed dacs  sound alike. What about a dac which uses a beefy analog power supply vs a dac which uses switchmode power supply? Will the dac can using better power supply have better sonics?
Will the dac can using better power supply have better sonics?
I'd have to write "yes", given what I was informed by Schiit tech support and that can be inferred from certain Yggdrasil literature.
Btw the fair way to break in components is let it break in at a friend's place. When ready then listen to it. I have bought digital stuff before and almost no need to break in.