You might also consider a used Genesis Digital Lens. This device was more sophisticated than the others mention above. They use phase locked loops to dejitter the incoming signal.
The Lens actually decomposed the incoming SPDIF data stream, discarded all subcode information (a useful jitter reduction technique by itself), buffered the audio data in local memory, and then clocked the data out the memory with a high precision local clock. The Lens then reassembled the data into a new SPDIF signal minus the subcode and output it to the DAC.
It also applied dither to the audio data to extend it to a user selectable 18 or 20 bits.
The Lens actually decomposed the incoming SPDIF data stream, discarded all subcode information (a useful jitter reduction technique by itself), buffered the audio data in local memory, and then clocked the data out the memory with a high precision local clock. The Lens then reassembled the data into a new SPDIF signal minus the subcode and output it to the DAC.
It also applied dither to the audio data to extend it to a user selectable 18 or 20 bits.