More power for my Duos?

David Berning Siegfried 300b: Simply amazing resolution, transparency, and dynamics. Never heard better along these metrics. No congestion with classical music. I also didn't think the amp was lean in any way. However, the amp is no longer made and my friend won't sell mine back to me. I regret getting rid of this amp. I would highly recommend this one for the Duos. I think it would suit your purposes perfectly.
Kronzilla SM: Full bodied and good timbre. This is my current amp. It's a decidedly warmer sound than the Berning. Also not as forward. The soundstage emanates from behind the speakers but is coherent and stable. I don't like the fact that it emanates from behind the speakers but others do. All-in-all a great choice if you like a warm, full-bodied sound. Again everything is relative. It's a neutral amp but is on the side of warm and full-bodied but not to a fault.
Viva Sentesi: Similar to Kronzilla but not as resolving and the top end seemed rolled. Everything else was good though, especially at the price point.

Hope this helps. Someone I know uses the Kondo Neiro's with great results (not surprising).

Hi BOA, I thought it was clear that the answer was that it was not your amps that were at fault but other components? Please read all e mails carefully.

The bass of a pair of Avantgarde DUO's can be substantially increased and improved by the following means:

replace the subwoofer cords with Cardas Golden reference Power cords. This really sounds both nutsy and (slightly) expensive, but it really works and if you have enough money for DUO's you probably have enough for the cords. I was opposed to getting pricey cords til I heard them first.

upgrade the external wires to DUO 3.0 Cardas jumpers - available only from Avantgarde. (if you haven't done that already)

much much more warm bass!!