One major difference between the Phonitor 1 and Phonitor 2 is the output impedance. I believe the original Phonitor (and Auditor) had a 9 ohm output, whereas the Phonitor 2 has a 0.18 ohm output. The effect a low output impedance like 0.18 has on the sound is a tighter sound character for lower impedance headphones like the Z1R. The Z1R is 64 ohm, so it might not be negatively affected by the 9 ohm output of the Phonitor 1. But with the Phonitor 2 you'd be comfortably below the threshold where the impedance mismatch would have a negative effect on the sound.
Apart from that the Phonitor 2 has lower distortion, lower noise, lower crosstalk, and is more powerful as well. Unless you can get the Phonitor 1 for cheap, the Phonitor 2 is simply a better amp. And with headphones of the caliber of the Z1R, the difference should be audible.