Pedrillo, the above two responses have summed it up well. The main problem with Avantgardes is that they do not sound good unless you sit a fair distance away from them - this is because the drivers are spaced so far apart. Sit any closer than 3m (9ft) and the speaker loses coherence. You can hear each horn as a seperate source. This problem is worse with the Duo's since the horns are spaced further apart. If your listening room does not allow you the space to sit far from them, then I would forget about either Uno or Duo and consider some other speaker instead.
The other problem with Avantgardes is that they are really DIFFICULT to set up. When I auditioned the Duo's, the dealer was unable to get them to sound right in his small room. Nothing he tried seemed to work, they still sounded incoherent. He just could not get the subwoofer to work with the horns. Very disappointing, given that he was the dealer.
They are very revealing of upstream electronics. If you use a second rate amplifier, the results could be disastrous. As I found out the same day with the dealer trying several different amplifiers.
But ... get them in the right room, with right electronics, and you have a killer speaker. Remember, good sound is 1/3 gear, 1/3 room, and 1/3 YOU. Good luck with your quest :)