There is MUCH more variability in the sound of tube gear than there is between high end solid state gear. For my particular taste, there are many high-powered tube amps that I don't like--many sound hard and brittle and less "pleasant" than most solid state amps. But, this variability means that, with a diligent search, one can find a suitable amp; it just takes a bit of effort. I tend to like lower powered tube amps, but the concern being voiced here is with how difficult a load the Moab might be despite being relatively efficient. I've only heard the Moab being driven by solid state amps, so I don't know how significant are the concerns raised above (I liked the speaker, by the way).
Still, it is probably worth your while to look at some low to medium powered tube amps. I agree with the poster above who suggested the Audio Note Oto. I really like the sound of that amp and it seems to work well with a wide variety of speakers. The only big downside for my purposes is the lack of remote control of volume. Audio Note also makes another very good sounding integrated in the Soro (6L6 tubes).
My favorite brand of integrated amps are models from Synthesis Audio (Italian). In particular, I like their 40 watt A40 amp (pushpull KT 66 tubes) which includes a very good built in DAC and has remote control. The bigger, and more expensive A100 (a quad of KT 66 per channel) is also very good and perhaps more suited for a demanding load.