So can Vic or Ken give the M6 a relative warmness to say the LMII or TF550.
Warm is such a nebulous term. In the loosest sense, I would call all three of these heads 'warm' in that they surely aren't 'hi fi' or sterile.
In the stricter sense of how I use warm, which really resides in the mids (i.e., a smooth mid tone with plenty of low mids and a somewhat polite and organic upper mid response, and also a 'sweet' treble response), I would put the TF550 on top, the LMII next, and the M6 quite a bit below. The M6, while having plenty of fatness down low, is just so aggressive in the upper mids and lower treble, that 'warm' doesn't really come to mind for me as much as grindy, aggressive, and 'in your face'.
As a point of reference, I would call the Walkabout and MPulse600 'warmer' than the TF550 and LMII, since they have all that low mid and mid mid 'tube wool' in their tone... very present in the mid mids, and a sort of bloomy low end that really says 'all tube' if you don't listen too closely.
So:
TF550... warm and tight
LMII.... even, relatively transparent and quick
MPulse600.... warm, big, fat and a little 'loose', 'slow/give'
M6... big low end, aggressive upper mid brightness, 'quick'