dotdash, you saved the day! :)
So it has been working all along, I just did not properly perform the ping test, when I had the VIPs set up with type Proxy ARP.
Thank you very much, your 4 steps showed the way to success.
BTW I had conversations with a lot of ppl today in various ways, and they all just told me, that this setup can not work properly, and that my best chances are to return to the former setup with the DSL modem handling the PPPoE connection. Now I can proof them wrong! :)