You report that the Sony has a toslink optical output but that you hooked up the Sony to a DAC using a RCA cable.
Either your Sony has a SPDIF/Coaxial digital output (and not just the toslink as you stated) or you have hooked up your analog output of the Sony to a DAC. This won't work. Not sure what the DAC is saying it is locking onto, if in fact it is an analog signal. Check again, does your sony have a coaxial digital output? This is one output that carries both channels.
you then say that you can hook up the CD to either preamp and everything is fine. When you hook up the sony to the preamps, I am assuming you are first changing where the cables are attached to the Sony before hooking them up to the preamp. If you are just unplugging the RCA cable from the back of the DAC and plugging that same end into the preamp - then you are not running a digital signal to the DAC, you are definately running an analog signal.
Either your Sony has a SPDIF/Coaxial digital output (and not just the toslink as you stated) or you have hooked up your analog output of the Sony to a DAC. This won't work. Not sure what the DAC is saying it is locking onto, if in fact it is an analog signal. Check again, does your sony have a coaxial digital output? This is one output that carries both channels.
you then say that you can hook up the CD to either preamp and everything is fine. When you hook up the sony to the preamps, I am assuming you are first changing where the cables are attached to the Sony before hooking them up to the preamp. If you are just unplugging the RCA cable from the back of the DAC and plugging that same end into the preamp - then you are not running a digital signal to the DAC, you are definately running an analog signal.