I installed RopIeee and the Raspberry Pi 3 is connected via USB with my AVM amplifier with built-in DAC. When in RopIeee settings on General Tab you can select a HAT. When I first looked at it it says ‘No HAT configuration’. In the list there’s also an option called 'Raspberry Pi DAC (I2S). After selecting that option in Pi reboots.
In both options Roon works. Which option is the best in my case?
In your case your Pi is connected with your DAC via USB. That means that the default setting ‘No HAT configuration’ is enough. ‘Audio USB’ should be enabled though, but that’s done by default hence you’re hearing something