Im wondering if it's possible to change the NUM PLUS/MINUS volumecontrol so that i can use the mouse-scroll instead?

Sure with foo_uie_volume.dll.

i have that dll but still doesnt get it to work

why when I change the volume effect of this change I hear after ~2-3sec but not immediately??

Because Volume is DSP component in Foobar and you can decrease it by decreasing buffer, but you cannot eliminate it. Is that such a problem? Use replygain and you'll hardly ever have to change volume anyway.

Case said this should no longer be issue with 0.9. Wait and see.

It sounds like you have a huge audio buffer set. If you decrease the buffer size to something more reasonable (few hundred ms), its a lot quicker. Though as richter said, I believe you'll have to wait for .9 for it to be immediate.

maybe someone could answer the first original question instead? =)
how can i make the mousescroll control the volumebar? i have the foo_uie_volume.dll component

When you have it in your sidebar, just hover it and scroll.