He's not specific enough for me to ascertain what exactly he's testing. If he's saying he can hear the difference between DACs, I'd believe him. I wouldn't be surprised if he hears a difference between the DAC in a CD player v. the DAC in a receiver v. the DAC in a better CD player. What I would be surprised and heavily skeptical of is if he claims he can hear the difference between CD players when outputting in digital.

But I can't tell exactly what he's compared.