I hope someone could clear up some confusion I have about s/pdif, usb and converters between them. I have a 2007 macbook pro with an SSD. I use toslink out to my bimby and also sometimes use usb with wryd. I thought most other computers have toslink too, so why use a usb/toslink or usb/whatever converter ? Is it because people using those converters just don't have an s/pdif output from their computer ? I'm not aware of any deficiency my 07 MBP toslink output would have and why its usb would have an advantage even if using wyrd.
Moreover, is it the actual input on the DAC side that some people prefer as opposed to whatever output method they choose from their computer ?
Computers parts (or as a whole) are designed with a low-margin / high sales volume in mind.
Every stones are turned, sometimes corners are cut, to design a product at the lowest cost possible.
Audio quality is never a concern for mainstream product (we wouldn't buy external DACs if it was).
Having features like optical or electrical S/PDIF outputs could be a marketing differentiation, but chances are high that the implementation will be on the cheap.
Given how polluted the power in a computer is, TOSLink sometimes yields better results than electrical transmission (like coax or USB), thanks to its inherent
galva electrical isolation (no ground loops, no RF interference).
The problem with TOSLink resides in its low bandwidth (6MHz), which result in higher transport jitter, compared to coax S/PDIF or asynchronous USB.
Cheaper DACs usually implement S/PDIF with off-the-shelf receivers (DIR9001, WM8804, AKM4113, ...), which cannot eliminate all the transport's jitter (in addition to supplying their own phase jitter).
More complicated techniques can be implemented, to alleviate these limitations (FIFO + re-clocking is a typical example), but they add complexity to the DAC, which in turn drives the cost up.