Is there an advantage to an external clock when the Aurender already has a quality clock and the May hasn’t any clock input? Is Silver critical with USB?
A 10 mHz external clock helps the internal clock be more accurate. It makes a big difference. It is not essential to have a clock input/output on your DAC but the Terminator Anniversary kills two birds with one stone.
Silver USB works very well for me but USB cables seem to vary wildly in performance to cost.
As @soix said put your best analogue cables on your digital rig and compare.
However you need a few months for everything to burn in.