As for Audio Out... from the manual, p. 51, "Audio Out is the digitized audio signal after the Amplifier VCA." -- I would think that you could think of it as a continually variable positive value of between 0 and 127 depending on the amplitude of what's coming out of the Audio Outs.
Random... I have always assumed to be a random value of 0 to 127, but I could be wrong.