I would think that bits would arrive cleaner by having a sort of wall between the noisy multi purpose computer and the dac. Optical i would have thought would provide this vs a usb which relies on an electric signal from the computer.
Yes, that is a potential advantage of an optical connection. However what you have found, at least in your setup, is that the potential disadvantages of an optical connection outweigh that potential advantage.
One potential disadvantage, I believe, is that the electrical outputs of optical-to-electrical transducers tend to have slow risetimes and falltimes (i.e., slow transitions between their higher voltage and lower voltage states, and vice versa), which can adversely affect the jitter performance of the subsequent circuitry in the DAC. Also, my understanding is that waveform quality, and ultimately jitter, can often be adversely affected by the quality, or lack thereof, of many optical cables.
It is telling that in S/PDIF applications, where digital signals are conveyed from a transport to a DAC, coax connections seem to be preferred by most audiophiles to optical connections.
Regards,
-- Al
