I'm not convinced that his "High Performance" SPDIF mod would do anything for a transport with a properly functioning SPDIF output. He basically replaced his broken SPDIF output for one that works.
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I played with marginal SPDIF signal levels decades ago and it can progressively degrade the audio quality to the point of very minor distortion, major distortion, then intermittent static in the music and dropouts.
I was experimenting with very long SPDIF cables making them longer each time while audibly noticing the sound quality degrade. I used various lengths of RG6X coax which is quad shielded 75 Ohm and more commonly used in low loss Cable TV (and satellite) applications but works fine for SPDIF. I was running a 5-Disc Adcom CD Player / Changer as a transport to a distant outboard DAC in another part of my listening room.
