40+ watts SET, cost is not a problem

Pani, I powerful single ended tube amp design could work out fine but you will need to find the one that gives you the sound you’re looking for.  Some can be very musical and full sounding while others can be very neutral. Me and my friend both own different 45-50 watt single ended 805 tube type mono block amplifiers. Mine sounds very full, large and musical. His, very neutral and accurate. Mr and my friend have been into audio for 35 years. I own about 12 amps and he has probably about the same. We been through tons of stuff. I agree that a properly designed PP tube amplifier can sound absolutely fantastic. I have 3 amplifiers setup in my living room now in 3 different systems. A pair of VTL EL34 mono amps 178 watts triode modified. The single ended amp, a 805 tube working with a 300b tube to get 45 watts power.  And last amplifier is a CJ 100 watt PP EL34 amplifier.  I can honestly say, neither one of these amplifiers is better than the other. They are just different in what they do and how they present the music. I also own a Canary 300b amplifier that is wired with silver and do not hear anything negative about its sound. In fact, it sounds absolutely fabulous. My point is, I own a lot of stuff. Me and my buddy have owned ton of gear and still do.  I thought as you did about single ended designs, and yes, they can be excellent but so can other tube designs.  

informative discussion, thx

Couple of questions:

re p/p- see lots of offerings with auto bias, not sure how much to trust this feature-anyone with experience pls share

Re atma sphere--are the m60 still available in kit form?

I have Klipsch Cornwall IV’s

What you are looking for does exist and can sound superb with your speakers.  

KR Kronzilla's would be an interesting choice.  The tube is esoteric but it sounds really good and delivers a lot of power.  Not exactly like a 300B but 300Bish. KR also makes a 40w 300B push pull.  

Alternative options that would be intriguing would be the Art Audio Quartets (845 push pull) and Opus 4 (Kt88 push pull) that deliver a very engaging experience.  They both use a small amount of negative feedback.   These are both 45w in triode.  Michael Bump did a review of the Quartets a few years ago.  Bob Grossman recently did a review of the Opus 4s.  Both for Enjoy the Music.  

The CANOR Virtus M1 monos are a KT150 based amp that is switchable between 0dB of negative feedback and 6dB.  They also allow for switching to Ultralinear and are 110w in that mode.  Several reviews have been done in Europe on these amps.  

Aries Cerat makes a few amps that are higher power and deliver what you are looking for.  The Concero 65 is parallel SET running the 813 tube.  The Essentia is a SS Amp that sounds very much like a SET and could do a nice job.   

None of these are inexpensive but all are stunningly good amps and will do okay with your speakers in that smallish room.  They either have 4ohm taps or in the case of the Essentia are stable to 1 Ohm.  

Full disclosure, I am a dealer for all these brands.  That said, it also means I have tested these amps in the real world.  I have publicly shown speakers as low as 84dB sensitivity in rooms about your size with the Art Audio and Canor amps and have heard the Kronzilla and ACs in similar spaces.  

You could also go with a more traditional design like VAC or a hybrid design from a brand like Riviera.  Any of these will shine like the sun with those speakers.  

 CAT JL5. Convergent Audio Technology 

This is so easy. The CAT JL5 can drive the smallest speakers with all of the detail and sound stage you could ever want. I just saw them at Axpona driving the new baby Clarysis Piccolo speakers. Also, my friend has olderCAT equipment driving his Tekton tower speakers which are pretty efficient. You did say cost is not a problem. The CAT JL5 was also used in the Aretai speaker room driving their book shelf speakers. Which are not hard to drive at all. The JL5 can work with anything.

The one thing I was surprised about is the run very cool for a tube amp even while driving huge speakers. 
 

Thats a nice problem to have, really superb equipment.

Already the predecessor R1 was outstanding however also demanding on the upfront chain but truly world class.

I may have a soulution for sale.

My thoughts are that there is one pair of Single ended that easily can feed the TADs

The older Siltech single ended power ampilifiers SEPA are giving out 80w/8 ohm real class A from a single nuvistor tube. 
A group compared them and the Kagura monoes mk1 and the Siltechs were clearly better and with an extreme lifespan from the nuvistor tubes also winns there.

They are however rare and were only produced in 15 limited pairs and actually not even set up for public sales but only for Silteck picked out distributors around the world at the sum of 130.000. Which with a normal profit factor would have had a retail price of around the double and in the Kagura area.

They weighted almost 60 kg each and all wire included transformers were the G5 silver/gold aloy from Siltech.

Only a few have be up for sale until now but soon I may put up a set and they can be testet in AB against a set of Robert Koda K70 mk2 which also are a outstanding poweramp.

Happy listening.