Just a word of caution. Optical connections tend to be poor. Typically they are add in functions and the component manufacturer just sources an inexpensive electrical to optical converter to do it. In general, these are not the connections people serious about sound quality would use. So, it is very possible what is coming through is more of how well the optical converter was integrated. I would use SP/DIF or AES for sound quality comparisons. Of course, then it is a question of how well the streamer and CD transports manufacturer designed and built their components.