Could someone recommend a next amp upgrade

ZU has an Atma-Sphere S-30. We have a set of Druids....

I think the M-60 really does the job on the speaker though. Impossible to clip the amps, and the ability to compete with a jet engine :) From Black Sabbath to Mahler the system plays anything you can throw at it at levels that you hear in real life, but musical at the same time.

You may also want to look at a REGA CDP, but even playing with some different interconnects and possibly speaker cables will suffice - interconnects can have a huge impact on the sound. The Druid/ Onix combo should be a really nice match - maybe a non-tubed CD player like Rega or Naim might smooth out the revealing aspect and warm it up a bit. I use an old Rega Planet with tubes and it has a nice tone but does not go over the top - however I have heard the Jolida CD player is very nice too, but again tubes. Also maybe consider Undewood Wally, he does a mod for the Onix - that might be a way to go as well. Hi-Fi+ just did a review of the Melody/Onix and they gushed over the thing - they could not say enough good, 6moons too, I dunno, sounds like you have a nice combo to me. If you change, maybe Naim is a good direction for you, I would have a listen to Naim if you want to consider something new. The Nait 5i is pretty nice and plenty of power with the Duids. Detail would drop but it would punch like crazy yet still have a warm feeling. You have options.

upgrade your CDp to a modded unit ,Trichord Research has got a smoking new Clock-5 module coming out very soon ,connected to their super never connected power supply module will be one serious combination for under$600
that would be a solid step up for your cdp.