I have a pair of Duos at home (paired with Tron Meteor and Quad IIs). The Duos are so efficient, you don't need more than 4-5 watts. However, whatever you use must be quiet and good as the Duos are very revealing. I have heard the Duos with the Tron PX25s (5 watts) - sublime. I agree with Ejlif - play around with positioning and subwoofer setup. that's crucial. Mine were set up at home by Graham Tricker from GT Audio (UK distributor for Avantgarde and manufacturer of Tron amplifiers) - that's part of his service in the sale price.
In my room (35 x 20 feet - 12 foot ceilings), the subwoofer crossover freq is set at 170 and the volume at the 12.30 clock position.
In my room (35 x 20 feet - 12 foot ceilings), the subwoofer crossover freq is set at 170 and the volume at the 12.30 clock position.