Fanless CPU heatsinks are good if you have a relatively low powered processor:
https://www.fullysilentpcs.com/product-category/cpu-coolers/?v=7516fd43adaaThese are actually HUGE heatsinks. However, they are not good enough if you're running a 12-core CPU for gaming (like me).
I tried Fidelizer a long time ago and it actually did weird things to the audio on my desktop (in other words, it did not improve it). It did however improve audio from my crappy laptop, so verdict is out.
I have found that running Windows with stock kernal timings seem to be the best. In some cases, the windows WASAPI drivers sounded better than kernal streaming from JRiver. lol. If I was doing a dedicated music server, then I would look at Euphony Stylus and doing a closed silent PC with a relatively lower power cpu. However, I have specific needs for a general use computer that has to server as a miscellanous platform, gaming platform and music playback along with data redundancy for all my personal financial data (quickbooks, etc.). So I had to pick very specific parts when building this.
So now I focus on how good the sound card is and how good the power supply is. The Pink Faun S/PDIF with Farad power supply is just excellent! I will eventually add on their custom OCXO clock, which should give me significant improvements.
NOTE ON PINK FAUN: There appears to be a compatibility issue if you run Pink Faun card on a Linux platform using Intel CPU (sound breakup problems). This is a weird problem with the chipset used in the Pink Faun card. Pink Faun engineers and Linux engineers have worked on this issue for many years but nobody can figure out the root cause. Intel CPU with Windows appears fine though. There is no issue with AMD processor and general consensus is AMD actually produces better sound as a digital transport.