I heard 909 in a several occasions with Quad Electrostatics (2809, 2909). I was surprised how well they were playing together. My impression of 909 is that it is very fine, neutral sounding amp. This "neutrality" maybe opinion-divider, because it does not really put much into the music - it just let it through ... It seems to me also that it is a great bargain. But probably it should be heard first because just like all the others, its sounding depends on the speakers and synergy with them ...