Whats the FATTEST sounding Tube amp to warm up Lean speakers?

Whatever tubed amp you choose, load it with NOS British valves(Mullard/Brimar/Ediswan/Genelex/etc).  If those don't warm/sweeten/fatten things up enough, swap it's resistors out for carbon compositions, and/or- it's coupling capacitors, for oil in paper types.

I'll go as far to say it's not the tube amp but rather your choice of tubes. Vintage little Mullards are extremely warm sounding. Vintage Tung Sol 6550's solid plates are warm like Mullards but with the EL34's glorious mids that are known for but with a lot more low end and power. I was never a fan of current production tubes. I had the Octave V70SE and later the V110 with a black box. I even had the V40SE for a short while. All were good but as you move up the line you gained more 'control' of the music.

Agreed on the NOS Mullard EL34's. They are what I have in my Shindo Montrachet and I couldn't be happier.

The late designer of Merlin almost exclusively used Joule-Electra OTL amps at trade shows. You might want to contact Rich Brkich of Signature Sound, as he knows Merlin speakers as he worked closely with the designer.

Sure- the Jouls is known to be a favorite match by the designer, however, im trying to counter the speaker's philosophy here, so it is my thought that the Jouls is actually going to emphasize the leanness of the speaker, not counter it. Or Bobby P wouldn't have used it.