I switched from a Spectron Musician 2 to Rogue 120 Magnums (I will be sending the 120's to Rogue in the upcoming week to be upgrade to 150's), driving modded VR4's.
I prefer the sound of the Rogues (particularly with NOS GE tubes) to the M2 amp, and I do not feel that they need bi-amping. Well, I was thinking of bi-amping them until Albert did the mods on them. This really made them very tube friendly.
Keep in mind that the Spectron will probably have a different sensitivity than the other amps you are looking at, and thus you will need to attenuate the sound of the tubes. I say that because most likely the tube amps will be more sensitive; that was the case compared with the Rogues. So you will need a crossover or at least some passive attenuator, like the Axiom pre. This also means more cables, more connections, etc.
KP