Today, I received the additional counterweight and also the 2x Powermate. I tried both - yes, it was finally clear!!
With the counterweight, I can finally balance the scope with all the gear (guidescope, starfinder, camera) in the back. Good!
Then I setup the scope, aligned and too photos of M27 with the Powermate. Turns out, that the 2x magnification together with the light pollution filter requires quite long exposure times. Here is the photo with 4 min exposures:
Not very sharp and not much light. I should try it again with longer exposures - but for that I'll have to polar align my scope better.