There's a few upgrade options for the DAC chips too. Comes with a Cirrus? I think.. Not been a fan of Cirrus since i-Gadgets started on them and their SQ went south..
but also a Burr-Brown chip or 2 options I read. And all the fun and ease of changing and rolling just a single tube.
Not sure how many tube options there are but I'm the 1st to say I'd be looking right away for some obscurr Russian tube out of a 1970's Bear Bomber or an Amperex out of a British tube radio from the 60's.
I never understood, however, why oh why they couldn;t make their tube an easy and everywhere 12ax/y7?