Anyone listen to Zu Audio's Definition Mk3?

Spirit,

You can do better then Atmasphere IMO. I mated it to my Superflys which were a more favorable 16ohm, and despite wonderful transparency and great bass they were pretty lean and analytical.

Follow Phil's suggestions and go big big bottle SET. There are great options on the used market that will be much better then the atma.

I've never yet heard a tube amp to sound lean and analytical, BAT gear esp. always strikes me as too lush and warm.
At this point in my audio quest I have struck a good synergy between Hovland tube/SS and the Def4s, and so have to make a decision to investigate OTL Atma Sphere/Dave Berning, SET Audion, Tom Evans Mastergroove upgraded phono stage or Soundsmith Straingauge cart, or working on system wide improvements (supports/cabling/power). At present can't afford all three.

I differed with Gopher on the Atmas with Soul Superflys. I thought they were a great combo. But I was coming from the SS First Watt world, and wanted to retain some of the First Watt qualities while getting the benefits of a tube sound as well. Gopher went to the big ole 845 tubes, IIRC. So personal prefs will come into play here.

If possible, I'd try to compare the big bottle SET tubes with an OTL design.

My Hovland HP200 tube pre/Radia SS power amps are showing a good synergy with the 4s, and I'd really need to be convinced of the benefits of all tubes to make the pricey step up.
In the UK it's getting harder and harder to make meaningful audio comparisons, so I have to grab auditions when I can.
If I move from the Hovlands, my likely alternatives are the Atma Sphere S30/M60/Novacron or Dave Berning OTLs, and Audion Black Shadow 845 SETs.
Simon, the UK distributor of Zu really rates the Atma S30, maybe this is where I'll end up, certainly will be my easiest to arrange audition.

Gopher,
Your big tube SET vs OTL comments are astute.These are two different camps for sure.Preference and system will determine which direction to go.
Regards,