I agree with Mike, the new XD series are significantly better.
I was a bit affraid of new D class amps cause during the listening of Duo Mezzo g2 in Avantgardes HQ last year I auditioned the latter with amps in Class AB and liked it very much.
But in reality new amps with DSP control gives the opportunity of adjustments to your room, taste and the other elements of the setup.
The proprietary AG software available online works very well , the memory allows up to 80 different settings.
I liked my Duo Omega G2 very much , but the possibilty of fine tuning was reduced and sometimes it could result in the lack of coherency . It was not my case, friends who visited me liked the speed, dynamics and life like presentation of my Duo Omega G2. To reach the synergy of the setup the selection of amps, sources and cables was critical however .
Now with Duo Mezzo XD the influence of cables and tweaks is less evident, I have different settings of bass satelites for analog and digital, to change them is very easy on the rear panel.
Bass influences very much the reception of midrange and highs and this is a new experience for me, this is not just bass itself, the whole presentation changes .
If money is not the main criteria, I would go for xd series, but Duo Omega , Grosso or Mezzo g2 are very good options for money.
One remarque to Elberoth post: Mezzo is only one specific model within the Duo G2 range which consisted of Duo, Duo Omega , Duo Grosso , Duo Mezzo and Duo Primo. Now it' s reduced to Duo XD, Duo Mezzo XD and Primo XD ( Primos have double bass sections compared to Mezzo).
Duo Mezzo and Primo are the only models with so called short basshorn satelites, the other models have standard subwoofers. As far as I know some folks upgraded their g1 series to g2 specifications but the upgrade from g2 to XD is hardly possible .
More info at Avantgardes website:
http://www.avantgarde-acoustic.de/duo-grosso-product-en.html
I hope it helps,
cheers
Mariusz