All vandersteen users ?

Depends on the size of the room and how loud you listen. I have 3A signatures and power them with a AR Classic 60 in a small room at moderate levels. I have no power issues. I will say I haven't tried them with a higher power amp so I don't know for a fact it won't be better, but I prefer tubes and eight 6550s are enough for me!

I've always used between 100 and 250 watts of ss power with my 2ce Sigs & 3A Sigs. Other than the sound of the amps, I didn't notice any difference in "headroom".

If you go with the Quatro, I would imagine you wouldn't need quite as much power, since they have their own powered subs.

Not a Vandy owner, and would be interested to read what others have to say. But I have recently moved from smaller to biggger amps, and have been pleased with the relative effortlessness and lack of congestion I seem to hear, at least with less efficient speakers, even where I hadn't sensed the effort and congestion before. Still, I would imagine wattage is not the only, or even the main reason. Bigger power supplies help dynamic headroom and transient response greatly, for instance. Damping factor important too. Anyway, it must certainly be true that if the first watt isn't good, it doesn't matter how many more you have. Of course room size and musical preferences (and damn near everything else) matter too. But my experience has certainly been that, other things equal, bigger equal better, and decidedly not just louder, for amps.