Seems to be a lack of interest in this topic based on my receiving only two responses both of which are from retailers selling servers.
I have been doing on-line research and, outside of some signal manipulation options offered by a few of the upper end servers, I have not read about any specific reasons that a $10K+ server is necessary for improved audio, particularly if Roon is the primary music source (both streaming and playing stored music files) and especially when using an outboard endpoint (or renderer/streamer) so the core and endpoint are not located within the same box.
It seems many use Roon’s own Nucleus and/or Nucleus+ successfully in even high end systems (e.g., John Atkinson uses a Roon Nucleus+ in his review system). However, the Nucleus+ is no longer available from Roon (although the less powerful Nucleus is available) and Intel will no longer be making their NUCs (Next Unit of Computing).
In my world, where my main digital source is through Roon (either streaming or playing my own music files), a relatively powerful but not too expensive server solution similar to the Nucleus+ or SGC’s sonicTransporter i9, along with a high quality outboard endpoint, seems to be the answer. Another reason not to overspend on a server is that no matter what server I purchase, I can be assured it will be obsolete in about 5 years. Just look at the history of Antipodes’ many server upgrades (I still own the former flagship DX3). I am also going to look harder at the option to position the server near my router and the endpoint near my DAC and the rest of my system. I can connect a high quality switch directly to the router and then wire both the server and the endpoint to the same switch using an isolator such as fiber or one of the Network Acoustics filters just before the endpoint.
Based on my reading, the important features of a server are that it is dedicated to the audio system only, the processing is fast enough, the power supply is sufficient and quiet, the unit is fanless, and the OS is preferably some Linux variant, which many of the successful servers use for music. On-board SSD file storage, easy storage of ripped CDs, easy transferring/storing of music files, headless operation, and responsive upgrade/technical support are also be important to me.
I am still interested in hearing from folks who have found reasons they believe spending north of $10K on a server is necessary for great sound. Based on my current understanding, I will look at spending that money elsewhere in my system.