Adjust all sliders simultaniously?

[Wibs]

Hi,

I can't find a way to set all sliders to some specific value together.
Say, I have 512 single channels and I want them all to be set to 4 - how do I do this? Next scene, I want them all to, say 15.

I can select the sliders, but as soon as I click on the value to change it, it gets deselected.
I can not adjust the values in a scene builder for all, since there the dimmer is on a scroll wheel and it is in %, not in values.