As far as USB goes, it really depends on how good the USB receiver board is within the DAC. If is is using an Amanero board, then you can definitely get really good sound out of a USB connection. The Amanero board has to receive the USB data and then clock the data at the proper samping rate before sending i2s data to the DAC chip.
Of course, a cheap USB cable is going to sound crappy just like S/PDIF cables.
With S/PDIF on the other cable tables, the A10 has to clock the sampling rate and then send the pulses in exact timing for the audio file (such as 44.1khz, 96khz, etc.).
You can get some pretty damn good S/PDIF cables (think Nordost Heimdall or better, or Transparent Audio or Purist Audio Design.
Of course, a cheap USB cable is going to sound crappy just like S/PDIF cables.
With S/PDIF on the other cable tables, the A10 has to clock the sampling rate and then send the pulses in exact timing for the audio file (such as 44.1khz, 96khz, etc.).
You can get some pretty damn good S/PDIF cables (think Nordost Heimdall or better, or Transparent Audio or Purist Audio Design.