New Linear Parasound Halo JC1+ monoblocks, an even more improved new John Curl design

And they sound amazing with my Apogee Duetta Signatures.

George

What about these. Apparently Underwood HiFi has a few monoblocks FS

Ampzilla 2000 is a 300 watt mono amp that is stable into 1 ohm loads. Reviews have been superb In the The Absolute Sound product of the year review they said: "The combo (of amps and preamp) is far from inexpensive though that figure does include two excellent phono preamps and a headphone amplifier. Reflect too, that there are competing electronics exceeding $100,000 that give you far less of everything." The entire circuit is fully balanced from input to output and includes a unique new unbalanced-to-balanced converter for single-ended inputs.

• 8Ω: Minimum 300 watts, 20Hz-20kHz
• 4Ω: Minimum 540 watts, 20Hz-20kHz

THD and IM Distortion: 4-16Ω less than .05% @ any power level up to rated at any frequency or combination of frequencies between 20Hz-20kHz List price $10,200.00 Sale $5,100.00/Pr in blue Ambrosia preamp

I have a pair of the Zillas (from Walter) in house right now. Very good amps. Apparently Bongiorno was better than Curl back in the day on amps, the reverse for preamps. They are arc welders.

That said, I am curious on the JC1+ as in JA's latest Classe review he said the + is the more tube like amplifier. I don't think the original JC1 was known to be particularly tube like. Problem is $17k for amps built in Taiwan is a struggle for me when the originals were half that.

Not knowing this amp because of lack test measurements, the best thing I think Bongiorno did was the old Sumo Nine and later Nine-Plus ss circlotron type Class-A amps.(needed the input opamp changed to something better, also the output transistors all 20 of them if you wanted to go all out) 
https://6moons.com/audioreviews/thorens/sumo.gif

No independent testing done on The Ampzilla 2000, yes the manufacturer gives the 8ohm-300w and 4ohm-540w, but no 2ohm figures.
I've said this before a few times now, it's fine to say an amp is "stable" into 2ohms, it does not mean it can "drive" it, just means it won't oscillate and blow up.
But so is a little 1980's Nad 3020 30w integrated stable into 2ohms, but that doesn't mean it can "drive" 2ohms.

This is what counts, for "driving" 2ohms. (almost doubling wattage) Independent test on 8 4 and 2ohms  from the original Parasound Halo JC1 Stereophile.

all at 0.15%
450W into 8 ohms
850W into 4 ohms
1300W into 2 ohms  

Halo JC1 is a current powerhouse 1khz dynamic tone bursts, it can do
586.5W - 8ohm  
1154W - 4 ohms 
2255W - 2 ohms!!
and no less than 4200W into 1 ohm!!!!!!!!!!!

This is what you call able to "drive" 2ohms and be stable!
  
Cheers George  
 

     I've owned the JC1+ monos for a few months driving my Wilson Sasha 1 loudspeakers.  They pair very nicely with my ARC Ref 6 preamp.
They replaced my Levinson 33H monos.  Very dynamic and extremely
quiet.  Seemingly unlimited  power reserves.  They also do not generate as much heat as the Levinsons and are about half the weight to boot!   Very happy with the move.