There is a very sad and likely very incomplete history of the Doll / Fleischmann transition to be found on Ventix's website.
Fleischmann und Doll Dampfmaschinen und Antriebsmodelle
He also includes links to a Trix website that appears to have a very parallel history shown for that company, which seems to include Bing.
Then there is also this highly personalized account from a granddaughter that was written just a couple of decades ago.
Toy Electric Trains and the Holocaust
He also has a link to David Curtis's webpage which apparently once held some significant historical information, but with David gone sooooo long now, that link leads nowhere!
Hope this helps some.