The 2/90/2 is basically the evolution of the 2150 to a 2 rack space deal. It got a ton of good low end an umpf, it nearly impossible to overload the input stage and it will maintain headroom till your ears bleed. I would not state that that it is way different to a PS100 until ungodly volume levels.
The PS is headroom all day long too.
The 2/50/2 is a different beast, it's way more like a powersection of a tube -head, it starts producing compression and harmonics in reasonable levels, tight, but has some cool mojo. (My favourite)
Hated the Synergy, sounded dull and muffled. No idea why.
Never had the chance with the LXII, but after the Syn50-50 I'm not really interesed, due they share the same DNA.