USB vs Optical
I'm wondering how many reviews and user experiences have been optimally set up. IME using async USB with a bespoke driver is the best way to connect a PC streaming source, but it must use the proprietry ASIO (or similar) driver. The dacmagic+ is miles better via ASIO USB than optical, the Qute best via its own driver, and for me as was the NAD. Most of the DACs I have tried will work without their own driver but sound inferior. Interestingly, the most disappointing was the M-DAC, which had none (though rather amateurishly suggested downloading asio4all: I didn't, and thought that was a bit cheap in a £600 piece of kit).