just sitting here and try to blackout backgrounds with the use of a flash,

- simple just reduce distance to subject and increase the shutter speed

Now I want to have nice soft light and so I use a shot threw umbrella.

- does not work, you need to block the light partwise, since umbrellas spell the light in every possible direction. Does not work, since the background comes to a black grey in the best case

So I tried to gobo the umbrella, which basically did not work, there was a difference but not as much as I liked it.
Afterwards I tried a reflective umbrella, which can did provide the same result as before, so no help either.

Result?

a) use only hard light
b) get your hand on a softbox (easy) and a adapter to connect it to the falshes (nearly impossible)