Use your ears...
Want better or different sound? Spend the extra money on better speakers, room treatments, make sure you have plenty of power, or play with your DAC / Pre-amp, get a subwoofer etc.
Computer has one job. Deliver bit perfect data. If you use a little DSP with Roon (as I do), make sure your computer/server/whatever you decide to call it... has enough processing power so it doesn’t bog down. Maybe spring for a solid state drive.
Love Roon however, I went in with other audio nerds early on for the lifetime subscription on a group/gift offer Roon had going. Saved some cash there.
My server uses Linux, and fortunately the mfg (Salk) provides incredible support and made sure the latest update would work as it was a bit more of a change.
It also won’t shock me someday if like most computers that I will need something new to continue to run Roon. This isn’t because of owning a particular brand, but after years of buying nice Apple (or insert brand) computers, they all seem to "outdate". (that is an entire other subject). I hope this isn't the case, but it won't shock me.
But, feel free to drop $7500 or more on a dedicated audio computer if you like, it’s not my money! (but I would spend it elsewhere in the system...)