USB directly off the RPi is generally described as ‘noisy’, so most people looking for better sound quality use one of the HAT boards.
Two popular HAT boards that provide a digital signal to a DAC: the Hifiberry Digi+ and the Allo DigiOne. Both have digital coax connections and the Digi+ also has an optical connection. Neither has USB.
Popular software choices are either Ropieee or DietPi. Both allow you to easily use the RPi/HAT as a Roon endpoint, controlled by your phone/tablet/laptop.
Personally, I have several RPi endpoints, all running Ropieee. I have not used DietPi, so can’t comment on the differences. Ropieee has been very easy to install and very stable.
We have two of these endpoints feeding DAC’s, one is a DigiOne, and one a Digi+. Both work well, but I would give a slight advantage to the DigiOne from a sound perspective.
I would second Sean’s suggestion. The Sparky is well made and the USBridge HAT is specifically designed for USB DAC connection. It would be a great place to start because it would be a complete solution.
I run two Pi’s directly off their USB ports, not hats. My DACs have XCOM USB inputs which filter out all the crud. I’ve tried hats and external power supplies with no noticeable differences.
As to the software, Linux is Linux, just the ease of use changes. I use DietPi on my Pis and stock Debian on my server. If you don’t know Linux DietPi is good as is RoPieee.
I too use the USB port of a Pi directly to the DACS of the active Kii Three speakers. Never noticed any noise. Superb sound and virtually empty audio rack…