I have MG 1.7's with the prologue premium and have used both EL34's and KT-88's, no issues with playing loudly. In that 42 watt situation I am much happier than I was with the Musical concepts modified Hafler DH-200 which stock had 100 watts. It is a fact that maggies are inefficient and playing full orchestra pieces will tax the amp but tube amps clip much more gracefully than solid state amps.. about the only time I have ever heard clipping was in the low drum or pipe organ bass notes maggies don't reproduce well any way. Prima Luna has also just announced that their full line can handle the Kt-120 power tubes... while these may not deliver their full 60 watts of power in an amp not originally designed for them, in a KT-88 amp they are reputed to still have more bass slam and definition as a drop in replacement for KT-88... mine arrive this friday.
So go for it, it will be a quantum leap forward compared to the NAD
So go for it, it will be a quantum leap forward compared to the NAD