Picking a Roon Core machine is an interesting problem. You can buy say a Sonic Transporter or a Roon Labs provided one. There are many others.
You can use a conventional desktop PC or MAC. You can build your own.
There are a lot of variables and some of them may effect sound quality. One example is the PWM fans in some computers add noise. Or the power supplies might effect things. Other issues that people address is operating system adjustments or running dedicated OS variants that help.
In my personal case I have been running a Sonic Transporter that works very nicely. I am playing with Audio-Linux as an OS and have been testing with a Linear Power Supply on the server. All of this has lead me to designing and building my own server. The parts are coming in now and I hope to build it this week. Will it sound better? I hope so! I just do not know till I build it. This is not a commercial venture for me, it is a personal mission.
I get to tinker with hardware and software along with listening to great sounding music. A lot of fun for me. Maybe not so for others.
If you are going to be running Roon with multiple endpoints and DSP make sure you have a reasonably robust server.