Wow...this is really interesting. I am enjoying this trip into cutting edge front end technology. At the same time, I am reminded of the relativity of technology as it relates to sound and how we listeners use it toward our own ends. In each step my system has taken, it is always from a place I thought was so satisfying, how could it get so much better? But it does! And from this thread and Pale Ryder's recommendation, the very inexpensive Fidelia player's advantages over the iTunes I had been satisfied with...may be yet another little "leap."
Like Brett, I love this hobby! And the microscope analogy....the importance of the first lens being like the source in audio systems, hyper important since its attributes are amplified by what follows. I really like this, but with my system, I am also particularly attuned to his thought that each part is equally important.
And now, realizing my Mini/ZDAC source may not be in the technological cutting edge of data movement.... I was really scratching my head. Like Lon has indicated when talking about his satisfaction with his system, in part due to his beloved Sony 5400 disc player, and how it sounds better to him than anything else he has had, here I am, right now, with an audio system so beautiful that it has the ability to transport me into the
experience of music, and from the less than optimal Redbook Cd stock....it just blows my mind.

But the ZDAC, coming from years of experimentation with circuits, chips, clocks and all, by a guy who has proven to me I can trust his sound decisions, it all worked for me....my trust was well placed. And regardless of theory, to my mind and body, it is a very good beginning in a system for which I can't possibly distinguish between the importance of one part over another!
The Mac/ZDAC is followed closely by the Zstage and its circuits and tube doing its "filtering," refinements, and enhancements; then the Torii and its many tube stages doing their part, and with my preferred tube sets in place; then the MG944s......with Decware interconnects and speaker cables tying it all together; and an assortment of power cables I moved around to suit my tastes; a bunch of Herbiesaudiolab stuff; and my room and power treatments tailored to suit my tastes........And last, but not least, all of it was designed by and built by three people working together toward a particular sound criteria.....Steve and ZYGI working independently, but interactively as Decware, and me working with their brilliant tools to make it all like I like it in my house.
As hard as I try, I can't think of a single one of these things that is less important than another to my system, and each improves on my very revealing and musical source, as the source improves the rest.
So, the nature of good tube gear and stuff designed for it supports the source = first-lens theory, but once that source is a good enough, and if the rest of the parts are synergistic, then everything makes everything else better at the same time! In this the technical efforts that led to the system parts are not unimportant, but they are now integrated into a sort of living thing that is very likely much greater than the sum of the parts! What an awesome opportunity to be able to play the game at this level!!!!!
And what a great opportunity to share information and experience in this forum.....the questing music lovers enabling each other toward a more refined musical experience! Thanks guys, and I hope it keeps on coming!!!