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

OP, you didn't mention what preamp/amp you currently have in your system but if the equalizer did not solve your issue, a tube preamp can also add lots of "syrup" to the mix, sometimes even more than a tube amp.

Be careful what you ask for with the Merlins.  Along with fat, full and warm you most likely will also get slow and syrupy.  I have 2 pairs of Merlins and have run them with several different amps, including some older CJ amps.  With Premier 12's and a Premier 16 pre, for example, the sound I believe was as you describe you want.  But along with warm and full I did get a much slower sound.  Warmer tubes, like Mullards, accentuated it even more. 

Currently I'm using an Atma S30 with one pair and a Pass Int 60 with the other and like both more than the older CJ sound but that's me.  I don't believe you'll get to where you want to be with an OTL, but with Pass you might.  See if you can find an older Pass Int 30 unless you have a large room or play loudly.  Then the 30 will be under powered.

Good luck.

Interesting. How do you find the sound difference between the Atma and the Pass?

I agree with much of what has already been posted.  Finding the right mix per budget, I would aim a little higher on the power side to provide the dynamic headroom.  

I heard amazing things about your Amps and i am close to trying your s30.

Usually people use the S-30 with the TSM. The VSM needs a bit more power so the M-60 has been the preferred amp for those.