I have found that the Optical connection is very non reliable at keeping a good connection between a transport and a Dac. Sounds like your are having a similar issue.I would switch to something that would allow you to use a Unbalanced or Balanced cable.I use a RCA cable to a DIP (digital processor) then XLR cable OUT to a DAC, then out using analogue RCA to pre amp. With my setup the sound is like a warm turntable very analogue sounding and easy to listen to for extended periods. I use a McIntosh cd player as a transport and I run digital RCA to a Monarchy Audio DIP then out to a MSB Nelson DAC. The signal is ROCK solid. When I was using a Sony player with Optical it was not as good.