Usb or Optical

All things considered, USB should be better. It does depend on the interfaces though. Optical has the advantage of minimal electrical noise contamination, but is, in general, much higher in jitter. I have had very good results with an MIT optical cable but for your application USB is the way i would go. As I am learning of late, jitter has a serious impact on sound quality, much more so (i would think), than ‘noise’. I’ve now heard a jitter-free signal delivered to a familiar system and the difference when clearing jitter is to me, quite remarkable. To me it would suggest that the digital reconstruction filters of average DACs / digital interfaces get the job a bit messed up. I am now a believer that clock-timing is so important for best results.