I did not see your specific needs in your post, i.e., do you use Roon to stream from, and do you need a server to play stored files, either from an on-board drive or from a NAS?
If you use Roon, their own Nucleus or Nucleus+ show up in some pretty good systems (e.g., John Atkinson uses a Roon Nucleus+ in his review system). However, the Nucleus+ is no longer available from Roon (base model Nucleus is still available) and Intel will no longer be making their NUCs (Next Unit of Computing), so Roon will need to make changes to their prescribed servers/streamers.
Another option is SMG (Small Green Computer) which offers their flagship i9 based sonicTransporter Optical server for $3K (you may want to add a LPS), but you will still need a streamer.
One thing to think about before spending big money is that the lifespan of servers seems to be about 5 years before they begin to get long in the tooth (go back and look at the historical model changes and upgrades from some of the better recognized server/streamer manufacturers).
I have not heard or read any specifics of why it would be important to pay big money for a server, which is essentially a computer dedicated to audio. There are potential advantages to certain programing and sound shaping options offered by some, but in the mid-price range, it seems SGC would be hard to beat given that they have been making and improving server products for years now, and many report that their support is responsive. Things I have found to be important as I have upgraded servers include, dedicated to audio only, fast processing, quiet power supply, fanless cooling, and some Linux variant for the OS. Other things I look for are on-board SSD file storage, easy transferring/storing of music files, headless operation, and responsive technical support.
Streamers (or endpoints, or renderers) that work well do not have to be expensive. One thing to look at is connectivity (i.e., do you need I2S?). As a start, look at the list of partners on Roon's website and check out the endpoints offered by the listed companies.
I would spend more money on the DAC, as the technology seems to be more mature and IME, they have a greater impact on what you hear.