Higher End DACs

Extreme. I will not get in the argument about overkill, but

Custom Windows 10 Enterprise LTSC 2019 OS, Roon and Jplay playback software

That's the opposite of future proof. Custom mods of OSs and Roon is a VERY BAD idea. Sooner or later you'll get stuck with unsupported, incompatible SW. Basically you are choosing to depend on a very small developer group opposed to a very large one; a very small user base against a huge one. Bad Idea.

As mentioned above, try Lampizator. They have a range but the Golden Gate 2 might be best for your price point. Often come out on top on DAC shootout forum threads. 

Audio-Gd R7 NOS Ladder DAC. Relatively cheap, use the HDMI I2S input from suitable streamer. Sounds very analogue and very good.

Vacuum tubes in a dac truly add to th3 realism of a bigger soundstage
and image depth especially when having a tube rectifier converting 
the AC to dc in the dac. Lampizator makes world class dacs starting at just under $3k their New Amber 3 which got a 5 star rating in enjoy the music.com to their $26k Flagship Pacicic dac and several inbetween 
depending on Your budget.and will give you 2 weeks to Audition in most cases. When needing a a Digital cable I have tried everything under $1500, the Final Touch Audio digital cable, and interconnects are the best as far as naturalness Ihave heard to date 
the dac cable is retail around $850.
at least check out the information 
you would be glad you did after 1 listen.

For DAC/streamer you must avoid expensive product like dcs and mbs and you should start with well engineered product. For amplifier you can stretch as they may sound deferent compare to dacs.

I would suggest matrix dac/streaming x https://www.matrix-digi.com/en/products/321.html

Or DAC only like Topping D90.