Thanks Angelus for your answer. I have both right now, but (sadly) due to financial reasons I will have to give one back (thanks to the return policy). I was sure to keep the new Bösendorfer but now you really make me think about it! It is true: the vienna imperial sounds so different to my ears compared to the Synchron. In fact I privately made comparison recordings and sat down and listened to them. The VI is sharper, clearer, melodic lines are not so nicely connected as the Synchron. Also the black keys just sound better in the Synchron. But there are the other little problems you also adressed. Sadly the wah-wah thing really distracts the playing experience for me... It's just unfortunate. Not sure what to do now. IF... one would have more money :D It's amazing how well the VI held up!
I am hoping a bit that when I have a better situation to buy the full Synchron Bösi (before end of June of course) and get a more realistic sound. I mean it's obviously a great sounding piano - but so is the VI as well. As a student a decision is needed now from my side.