The Stereo 50 incorporates “trickle-down” technology from AMR, specifically in the form of the GMT/ZeroJitter system used on optical/SPDIF inputs.
This means timing issues from the source are eliminated by passing the data through a memory buffer and clocking out the data with a steady clock.
So as long as you do not need high-resolution PCM above 24/192kHz or DSD, using SPDIF is fine via optical or coaxial.
