Anyone listen to Zu Audio's Definition Mk3?

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,

Charles, excuse my ignorance, but what are the salient differences between the two tube camps?
I had never got on with tubes full stop, being totally put off them by the stereotypical over warm wooly sound portrayed by BAT eg. But seven years ago got bowled over by the tube Hovland HP200 pre and found this sounded great with the SS Radia amp, servicing my Pro Ac Futures 2, then Zu Def2s and now 4s. Just love the combination of tube liquidity and SS neutrality.
Interestingly the 4s are so transparent and revealing I'm detecting a hint of hardness/coolness which I attribute to the SS Radia, and am really tempted to investigate all tube. Let me say this hardness is only a hint and may well be eradicated by careful choice of cabling (considering all Zu Event) rather than amp change.
So we have SET eg Audion Black Shadow, championed by Phil v OTL eg Atma Sphere championed by UK Zu dealer/Dave Berning ZOTL, much favoured by Roy Gregory in the detailed review of the Def4s in Audio Beat.
How do their respective pros and cons stack up, esp. in respect to listening thru the Def4s, with a very neutral revealing front end (in my case direct rim drive tt with air bearing linear tracking arm Trans Fi Salvation/ Terminator T3Pro)?