When originally ordered, the R8 was requested without USB input but extra attention in other input circuitry to bring it near R7 standards was installed. 
For anyone considering using the USB input there is always a USB converter option. 
R8 DAC review here 
https://www.audiophonics.fr/en/dac-without-volume/audio-gd-r-8-balanced-dac-4x-r2r-dac-native-dsd-i2s-acss-amanero-fgpa-accusilicon-p-13211.html