I own the Metrum ambre which is essentially the same as the Sonnet Hermes and also own the upgraded metrum onyx with latest DAC modules. Cees who designs both the Onyx and Morpheus basically said the upgraded onyx sounds the same as the Sonnet Morpheus.
Anyway I've tried both Roon and Volumio and prefer the sound of Volumio using my above setup and I connect the ambre to the onyx via I2s. It's easy to swap the small micro SD card inside the Hermes to either use Roon or Volumio. I just burned the Volumio software onto a micro SD card from the Volumio website and it worked. Volumio is definitely not as polished as Roon (less options) however it is much more lightweight and no need for an external computer or other device to hold the Roon core. For me I don't need all of the stuff that Roon does and I preferred the sound quality of Volumio so it works for me. I'm sure others will listen to both and say the sound quality is the same which could be true in their setup.
Anyway you can try Volumio to see if it sounds any better than Roon and there probably is a free introductory period Technically Volumio is free but if you want to stream Tidal and Qobuz there is a yearly fee.