40+ watts SET, cost is not a problem

@paradisecom, yes, the Magma’s are monsters! The transformers are about twice as big as the ones on the NAT Audio Generators. The chassis is 26" long. The Magma M’s transformers are almost one foot tall!

The sonics are much more pleasing than the push/pull 805 Generators. Currently these high powered SET arms may offer the most value of high current/watts SET amps on the market.

My amp is a Shishido 805, which is the basis of the Wavac 805 (effectively the same).  I find it a truly stunning amp - I think there is an early review that pretty much sums it up.  What is wrong with it??  You would have to hear it, and then maybe you could figure out something wrong with it - I can't think of anything,  The amp is driving a pair of Altec 604 drivers in 9 cu ft cabinets.  Tons of power, and the amp has the drivers in a vice grip with regards to control and presentation.

The Wavac secret sauce is likely the Tango transformers, custom wound by extraordinarily skilled craftsmen in Japan for the Shishido design.  Hirata Tango for mine, ISO Tango and apparently Wavac for the later variants.  You can likely find response curves for the special transformers on the web - my book shows the output transformer flat from 30 to 40K Hz (0db down).  Also there is an interstage transformer, so no caps in the signal path.  A simple, yet highly competent amp using stunning parts.

Seems like nobody else has actually heard a higher power set amp like the Wavac, and yet they are fine saying they don't sound good, or it cannot be done.  Not sure how they feel comfortable doing that.  If you have a chance to hear one, then do so.  It might well change your perspective.

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.