I'm still using my Quad IIs. They've been rebuilt by Graham Tricker at GT Audio (maker of the Tron brand of british high end tube amps). I've heard the Duos with Tron's 300B monoblocks and 845 monoblocks. Both are very good.
The important thing about the Duos is that your amps need to be quiet with zero noise.
My tuppence worth from the UK
The important thing about the Duos is that your amps need to be quiet with zero noise.
My tuppence worth from the UK