AE,
I'm sure that there are lots of bad sounding older Toslink and SPDIF implementations out there. Some cheap less capable newer ones as well. I have only tried SPDIF and TOSLINK in recent years and from companies that have some focus on good sounding audio products. Not the best or most expensive, nor the cheapest mass market stuff. I have been pleasantly surprised with the results that I have heard can be achieved. Definitely better and more affordable as a whole than was typically the case years ago with many analog sources of the day. So there has been progress in my eyes. Of course, there is always a way to do things better. USB use for hifi digital (USB is a general purpose technology being used now for hifi audio its not designed specifically for that) is newer and not as mature, and hence probably more problematic I would think still. The question is always how much does it matter and for how much. I suspect USB will become more mature over time and add more value in future scenarios where higher resolution audio streams specifically are involved. But currently, in applications where TOSLink or SPDIF suffice, I suspect it is still more hit or miss. That will change over time though as things progress though I would bet.