Shahens: For me, the sound trumps debates about tube types, something I find not to be as pertinent to the sonic result as the circuit those tubes are employed in (including the power supply and output transformer). Thus my VTL MB-185 Sig. mono's, which also feature Svetlana 6550C output tubes like the C-J Premier amps (but aren't used in the same way, not being wired in ultralinear and utilizing less feedback, among other differences), can beat the little EL34-equipped MV-55 stereo (non-Premier) amp in every subjective listening catagory. This includes the VTL's superior mids and highs, not just the bass - the whole spectrum is simply more natural, transparent, and capable, be it tonally, dynamically, texturally, or spatially, and in all matters of resolution, cleanliness, and precision (which is as it should be for 2 1/2 times the price). It is also true that the VTL's are not as overtly "tubey" in character, but only in the senses that they lack spurious colorations and distortions by comparision, and are simultaneously more extended and authoritative - things you would expect from amps with more power and better, larger output transformers, and factors not having to do with tube type.
I say this as someone to whom the MV-55 came as a personal revelation at the time I got it in terms of purity of harmonic structure, spatial naturalness, and lack of 'electronic' artifact. I've tried to quit using the term 'liquid' (and 'bloom' as well, if I ever did), since I have no real idea what that means for musical sound, but if you define it as not being able to as easily hear the machine interposing itself between you and your music (as opposed to defining it like 'warmth', an overlay of which the VTL lacks by comparision - to its distinct benefit), then that would describe what I've heard since moving up from the little C-J, an amp I'm nonetheless still fond of, and whose relative failings are never too unattractive to love in spite of having gotten myself a better mirror.
Anyway, getting back to your point, whatever sonic differences may exist between the standard and 'XS' versions of the various Premiers could just as easily have as much or more to do with the fact that their EL34's are connected as triodes - rather than pentodes as with the regular versions' 6550C's - than with the two output tube types per se (BTW, that's a change the VTL's can accomplish at the flick of a switch with their own complement of 6550C's). I would fully expect any of the Premier amps to be more competitive with the VTL's in my system (the most natural counterpart being the 12's as I wrote above), but if anybody really feels that the MV-55 betters the 11a in any ways, then that assumption may not be as warranted as one might think. Anyone with direct experience comparing the VTL Signature mono's against similar-rated C-J Premiers in the same system is encouraged to chime in...
