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

Thanks. Went with Joule Electra. 
Sounds great. A bit noisy and a bit fussy but worth it for now. When summee comea ill need to replace them with cool running amps but for nyc winter they double as my space heaters. 

The very first amps that came to mind were:

Dynaco ST70

Conrad Johnson MV55 (I owned that for quite a while - very warm, rich tube sound).

And, believe it or not...an Eico HF81!

They are astonishingly magical little 14W amps that *sound* much bigger and tend to fill out the region you want to fill out.  They are lush, yet still have sparkle and snap.  I have an Eico and every time I put it in my system it really tugs at my loyalty to my bigger CJ Premier 12s.(I've used the Eico to drive everything from small monitors, to big floor standing Thiel 3.7s, and brutal low sensitivity MBL omni monitors, and everything has sounded fantastic).

They tend to run from around $250 for "just out of the trash can" condition but still working, to $1,200 if it's been refurbished and spiffed up (and anything in between).  But even the out-of-the-trash Eicos can sound fantastic (my pal has one too).

There's one on audiogon right now for $250.  You could grab it to see if it does anything for you, and if it grabs you, then there's an upgrade path.

Ah...just noticed dumbeat already made his choice.
"never mind...." ;)

Joule amps have been called many things, but lean is certainly not one of them. They would add what you are looking for, in spades, while also preserving solid bass, and dynamics. 

I bet CAT amplification would sound great with Merlins