https://www.stereophile.com/content/zu-essence-loudspeaker-measurements
Who said Zu are supremely good speakers.
Good grief, I swear every criticism of Zu speakers begins and ends with the fabled Essence measurements from 8 years ago. I suppose it matters very little to detractors that Zu retired Essence 5+ years ago and it bears scant resemblance to their current product line, but hey, one has to grasp the nearest straw available.
I run DefHeads (Def IV's minus subwoofers) and yes they are supremely good. I certainly understand that Zu are not for everyone, and that some have had bad listening experiences, but that just puts them in a club with, oh, every other loudspeaker.
To the OP, personally I would go cheap on the streaming DAC and invest in a good tube integrated that will accomplish your sonic goals listed above and give you tight bass on those twin subs. There's a ton of options for $5k, if it were me I'd be looking at Leben, Luxman, Audio Note, Decware, etc. I use a cheap Chi-fi fleawatt SET on my DefHeads and I love it, but the bass handling on it would not be suitable for Definitions.
Other resources for you would be the Zu Definition Roundup thread, and also Zu's facebook page where they recently posted a customer's experience of using Luxman with Zu. Also Zu would be happy to give you an amp recommendation if you call them.