Both of these digital inputs have the same specifications, but one uses light and the the other uses normal electrical signals to transmit the digital signal. In general, if there is a long cable involved and you notice a problem on the digital coax input (RCA wired) this coud be becase it picked up noise that can corrupt the digital signal so in that case try changing to optical. In general we use the digital coax for a CD player to leave the optical available for a TV input.
When should I use the optical input and when should I use the coaxial digital input?
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