Bricasti M3/M1SE

Keep in mind, dedicated audio servers are PCs that have been designed and optimized for audio.

If you want to retain your present PC, you might look into optimizing it for audio before investing in a dedicated server. Not saying you may not decide to buy a dedicated server at some point, but you expressed a desire to use your existing PC.

Highend-Audiopc.com out of Switzerland offers a software download package that optimizes a PC for audio. Cost is ~$120 USD. https://shop.highend-audiopc.com/collections/software/products/audiophileoptimizer

I came across the Audiophileoptimizer software product while perusing the Mojo-Audio website.

Benjamin also offers tips to optimize Mac OS X for audio. https://www.mojo-audio.com/blog/optimizing-os-x-for-audio-video/

I had a Dell Tower dedicated just to running Roon core and nothing else hard wired to my network.  A Roon Nucleus was a big and noticeable step forward.  The CX will blow your PC out out the water.  Not what you want to hear I am sure but PCs just have too much going on, have noisy power supplies, etc....

I have not tried tvad's suggestions.  They might work.  Not sure.  Certainly can't hurt.  

@verdantaudio, a question for you (and @sksos) about Roon Nucleus...

If one stops using Roon (ends a Roon subscription), is a Roon Nucleus device still usable as a server?

I don’t believe so.  There may be a way to override and load different software but I don’t know what it is.  Nucleus is a Roon device.

The Antipodes S30 (pricier I know) does have the flexibility to use a bunch of different software packages.  

While reading through another thread, and doing some research as a result, I discovered the SonicTransporter I5 music server, sold by Small Green Computer.

A nice feature of the SonicTransporter I5 ($999 including 1TB SSD) over a Roon Nucleus is that if you decide to cancel Roon, the SonicTransporter I5 doesn’t become a brick like the Nucleus, since the SonicTransporter I5 is pre-loaded with HQPlayer (embedded), Squeezebox Server, Plex Media Server and MinimServer (DLNA server) in addition to Roon Core Server.

https://www.smallgreencomputer.com/collections/audio-server/products/sonictransporter-i5?variant=208...

Since the Roon Nucleus and SonicTransporter I5 are both Intel i5 computers, I see no reason why they wouldn’t sound identical on a network.