The Zx and Z are identical, and the Zx comes with a control module. For 250 Ohm headphones, however, I would recommend the ZxR, which has a very good headphone amplifier. In addition, the Control Module is better, there is no difference in sound whether the headphones are connected directly to the ZxR or to the Control Module. With the Zx, on the other hand, the control module is simply no good, the headphones are noticeably quieter and the quality is no longer the same. That's why I switched from the Zx to the ZxR. In the meantime, however, I have switched to an external DAC/AMP with headphone amplifier, which is the best choice anyway and often a cheaper price for the same or better sound quality. It just depends on whether you need all the effects and EQ settings that the Zx(R) offers. However, I was very satisfied with the ZxR. I only bought the external DAC/AMP to get rid of the noise from the studio monitors. Sound quality is virtually identical between the ZxR and the DAC/AMP I have.