Avantgarde Duos: Omega or Mezzo?

I have Duo, never heard Mezzo. If I may, I would really try to audition first. I suspect Mezzo is a significant improvement, but you should absolutely take your room into a consideration. What size is it, BTW? Any room treatments?

Subwoofers I have not because Duos not go low enough, I actually measured them go down to 18-20 Hz. It has more to do with the optimal placement, in doing that for approx. 2 years, I have realized, that a main speakers placement optimal for imaging is not always ( as in never) coincides with the optimal bass reproduction
That forced me to use an active crossover and cut off Avantgardes at 80 Hz , everything below that is handled by stereo JL subs.
An overall improvement has been immense. I have come to a conclusion , that this approach is probably the only correct one.
In your case, I don't think the smaller room could accommodate Mezzos

Trios are very tempting, and there are incredible deals on the used one's from time to time.
I can't really comment on Mezzo's integration, but I do think, it should be easier to do, than with the Duos

Miguelito,
Placement is critical, first, you have to position for the best bass response in your particular room- could be tricky, since it might NOT coincide with the best position for the imaging. So you will have to experiment in your own room.
I can tell you though, that farther away they are from the back wall. the better the sound stage depth will be (duh!)
Amp matching- I tried a few, and not surprisingly, Lamm ML-2
SET amps are a match made in heaven. And it is well accepted choice from many other owners.
Owners also say, that Art Audio PX25 is another good choice, but comes with a warning- DO NOT deal with Joe Fratus who used to represent (actually to misrepresent) Art Audio, which is a British company, in the US.
I also tried Tom Eavans Linear A amp, which was good, but not as good, as Lamm ML2.
I heard very positive reports on expensive Audio Note amps with the Avantgardes, but this is not a personal experience