I think both would be fine with a low power amp.
The M22 will play louder than the M3, for sure - and probably have slightly better bass extension. The M3, however, will have a slightly "richer" more laid-back sound - which you might prefer if you are into tubes.
On the other hand, the tendency of tubes to have rolled-off highs might work quite well with the M22, since some consider it very bright (I think that has a lot to do with your room - I have lots of hard surfaces, so I think they may be too bright for my tastes). The very flat response and forward nature of the M22, coupled with that "tube-sound" may be a very, very nice combination.
I would consider ordering both, then sending the one you don't like back. They are both small, and won't cost much to send back. Plus, I'd really like to hear your impressions (as would we all, I'm sure).
Well... I hoped that my ambiguous advice was helpful... or not
P.S. I use vintage solid state gear, and I was going to buy the M3's - but after I priced decent looking stands, I went ahead with the factory outlet M40's - which are about the same price as new M3's with stands. Their bass extension is quite good, but it is probably even more laid-back than the M3, with a slight hump in the lower mid-bass... but I kinda like their "meaty" sound - because it doesn't come with the expense of non-existent treble - the high notes still ring like a bell.
