I upgraded from the PS Audio mk1 Directstream to a Mola Mola Tambaqui last year. I listened to both with an audiophile friend and found the PS Audio compared favorably with the Tambaqui. It was still a worthy upgrade but I was impressed as to how the PS Audio compared to the Tambaqui.
if you can get a used mk1 unit, go for it. I doubt you will be disappointed.