Hi Peter, I have only the non-MQA version of the original D90. Just looked into the manual: it doesn't even say which DAC chip is used! To my knowledge, the MQA version also uses AK4499.
I love my DT1990 more than ATH-R70x or DanClark Aeon RT... it's a very fine pair of headphones. You can get rid of their treble spicyness with a passive filter or EQ. And they are nearly indestructible.