Panel speakers are dipoles, sub woofers have a monopole polar distribution, so it is very difficult to integrate the two. The Bowers & Wilkins DM70 electrostatic hybrid suffered from this problem.
I once heard Audiostatic speakers at an audio show (can't remember the model) and was very impressed. Curiously the room was empty, so I could sit in the optimum position, have the system to myself and spent some time enjoying the music. In fact music was the sole topic of discussion with the Audiostatic rep - always a good sign.
Congratulations Johan on your DIY electrostatics. I knew a collegue who built himself a pair of electrostaic speakers based on the Ed Saunders series of articles in the Audio Amateur magazine. They weren't easy to build, but he persevered and eventually was successful. Me - I'm happy with my Quad '57s, but I take my hat off to you for building your own. Well done!
Did you wind your own transformers or did you use commercially available items? What value of turns-ratio did you use?