I would go for the Aesthetix, no question. Nothing wrong with Pass but once the "new" wears off of this acquisition and you settle in and listen day after day, you will appreciate what the IO and tubes do for long term listening enjoyment.
Linnlp12 comments about active versus passive are accurate. The IO is active but it's mate the Aestheitx Callisto presents a significant improvement in sound, a purchase you could make years from now with no penalty should you need the added flexibility.
That being said, I would prefer IO as stand alone solution and If two boxes are preferred, the IO with single power supply would still be the superior choice and clear performance winner in my opinion.
Linnlp12 comments about active versus passive are accurate. The IO is active but it's mate the Aestheitx Callisto presents a significant improvement in sound, a purchase you could make years from now with no penalty should you need the added flexibility.
That being said, I would prefer IO as stand alone solution and If two boxes are preferred, the IO with single power supply would still be the superior choice and clear performance winner in my opinion.