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.
Troubleshooting toslink input problems on DACs
I have two systems set up in my house, both utilize the Airport Express optical out to a DAC. Both started having playback issues at the same time, one system cuts out ever 5-10 seconds and the other sounds distorted or fuzzy every few seconds. Both DACs play fine when using USB straight from the computer, both AE play fine using the regular stereo out. Anyone have similar issues? Could it be a network problem, maybe a cable problem? I did purchase a new AE and tried it on both DACs and still had the same playback issues.