I‘d be a bit careful about your claim on InnuOS‘ use of DSP. It is directly counter to their minimalist philosophy on CPU power, which by the way leads to superiror sound compared to Roon.
In my experience, the clean up of both the incoming Ethernet or fibre signal as well as of the outgoing signal, whether USB, I2S, Coax or other is way more determinant for sound quality than the actual box chosen. And btw, optimal cables and filters are again box dependent. If properly implemented, and that is no simple ask, even a amcor PC or a simple Bluesound Node can be quite effective.