My plan is to continue using a reliable, well-built, server, somewhere south of $5K,
Part of the point is you don't need to do that, albeit I am not criticizing the choice. It's more of a matter of convenience if you want auto CD ripping and things like that. Roon works with any PC with sufficient horsepower to run whatever DSP etc. you want to use.
You won't get any sound bump from any choice unless you hear hiccups or dropouts caused by an overtaxed server, which you can easily determine with the processing speed indicator in Roon. I have a fairly powerful machine currently running at 60x, meaning I can theoretically support 60 streams before any issue.
Not everyone wants to build their own PCs, I get that. But it's actually not rocket science and you can build a well overpowered Roon server for $1000 maybe less if you have a PC with some of the parts already that you can salvage (power supply, case, the stuff that gets obsolete less quickly).
My personal view is people buy these pre-built audio server computers because they look cool. Which they do. But they're sold with stories of superior audio quality when you get to identical quality with the above plus your chosen streamer. [Repeat acknowledgment of theoretical possibility of streamers sounding different].
Anyway, I just say this so that when newbies search "what music server should I buy to use Roon" there will be some balance of opinion against those expensive, fancy servers that get obsolete within a few years due to ever increasing CPU, memory, and hard drive speed, when you can upgrade a standard computer for ~$500 instead of spending 4 to 5 figures to replace the whole fancy prebuilt server.

