Zu Druids low powered tube amp or high powered SS?

push pull tubes

You may do well to consider a few other potential amps.
With 12 Ohm resistance you have a very good candidate for an OTL amp. You didn't explain if you are committed to a SET.Otherwise you should won't need to limit your choices low power.Withan OTL amp the sound seems tome to improve upto a point with power a very well made superb amp in this category is Atmasphere. The amps I have heard with any frequency are the 60 watt and the 110 wpc models. They are very good known best as fast, i.e. blazing speed of transients, will not congest and crystal clear, neutral sound.
If want color-there is nothing wrong with buying what you like not what others dictate is correct.
If you do want a warmer sound for instance, from the Druids (don't ask me if that's even possible or a flame war will erupt.) You could try a powerful or moderate or high powered true Class A only Only Class A, no plateau. Assuming you are biamping the low end. Those type amps are rare and expensive these days, expensive to operate may require 220-240-volt, are literally hotter than aspace heater and weigh as much asa Rhinocerous. A good example of a moderate Class A would be the Accuphase A 60. You need very deep pockets for that though. As a group they can handle the resistance whereas the class ab amps which are ubiquitous and standard isn't as stable under load variatio. Even then a class A amps do best with lower impedance against 12 ohms they will be pushing hard.
The best choice is a warmish tube amp, if the problem is that they lack fullness. The CJ tube power amps are warm. Not inexpensive but there are plenty of them so they come up for sale used on a regular basis.
After a debate on the matter a year or more ago , I was informed by my friend with very sophisticated ears and a very knowledgeable audio lover, who's equal I have yet to meet, said that the Definitions are very good speakers. They have more than their share of woofers and are very full, indeed. More importantly they don't require equisitely refined and expensive electronics to make them a joyto hear. If you bought Druids because you like their signature sound. Even after you break them in whenever you think that is consider this. You are allowed to change your mind therefore.
Given that you would spend nearly as much changing amps, and of course any amount more than that. Why not move up to the Definitions. That would seem to be a logical choice to me.FWIW

SORRY DOUBLE POST ACCIDENT READ THIS IF YOU READ ANYTHING I SAID.

You may do well to consider a few other potential amps.
With 12 Ohm resistance you have a very good candidate for an OTL amp. You didn't explain if you are committed to a SET.Otherwise you should won't need to limit your choices low power.Withan OTL amp the sound seems tome to improve upto a point with power a very well made superb amp in this category is Atmasphere. The amps I have heard with any frequency are the 60 watt and the 110 wpc models. They are very good, but if want color-thereis nothing wrong with buying what you like not what others dictate is correct.
If you want a warmer sound for instance from the Druids (don't ask me if that's even possible or a flame war will erupt.) You could try a powerful or moderate powered true Class A only assuming youare biamping the low end. Those type amps are rare and expensive these days, a good example would be the Accuphase A 60. They can handle the resistance whereas the class ab amps which are ubiquitous and standard isn't as stable under load variation . Still a class A amp will be pushing hard.
The best choice is a warmish tube amp, if the problem is that they lack fullness. The CJ tube power amps are warm. Not inexpensive but thereare plenty of them so they come up for sale used on a regular basis.
After a debate on the matter a year or more ago , I was informed by my friend with very sophisticated ears and very knowledgeable audio lover who's equal I yet to meet, told me that the Definitions are very good speakers.They have more than their share of woofers and are very full, indeed. More importantly they don't sound like the Druids but if you still aren't satisfied with them after you break them in, whenever you think that has occured, consider this.
Given that you would spend nearly as much changing amps, and of course any amount more than that. Why not move up to the Definitions. That would seem to be a logical choice to me.FWIW

Bb - What is lacking and what direction do you want to push them? I wouldn't think 300B GENERALLY would be the best choice, as they are voiced toward the warmer side which the Druids are as well.

I have run my two pairs of Druids with Carver M1.5-t, also McIntosh MC225, Denon, Ashly, Hafler, some others. Plus... Bel Canto eVo 200.2.

The Bel Canto *by far* was the best match, just an outstanding sound. And the same with my PMC TB2+, SLS 8190, Paradigm Esprit Reference.

Also, I would highly recommend getting the Zu Libtec cables. That just took all those speakers to their potential, especially the Druids.

Steve