Forgive me for writing in english, i am writing on a english keyboard. i know im 11 years behind on this threat but this might shed some light for you this theory on the bernstein zimmer and fishhorn.
I grew up in Zell am See and spent my child hood around the thumersback/erlhof and haus gabi area. Before we left the country i had a few friends, one of which was related to the caretaker of the castle. I had been in fish horn about 5 or 6 times before the renovations. During this, my friend and i spent a few hours exploring the castle but also finding out quite a bit about the history of it. For example, its a little known fact that the wife of one of the luftwaffe officers decided to commit suicide by jumping out of one of the windows during the night that herman goering was kept at the castle.
Back to the Bernstein zimmer.
There was Gold kept at the castle prior to the Americans coming through the area. This was loot that was part of a small transport that came through zell am see before the end of the war by LKW. My understanding is that is the loot delivered was kept here until the trains came through and intended to be loaded onto trains at either bruck or Shuettdorf. It never came to this, and in the rush the SS left it behind.
This is backed up by stories I know from locals in both thumersbach, bruck and schuettdorf. For example, friends of my parents were sent to fishhorn between the abandonment of the castle and the arrival of the Americans in search of food rations. When he got there, the castle was left empty however no food rations could be found. He decided to search the store of both the farm (which belonged to the castle and is located to the north of the property) and the castle itself. There he found no food but several cases of weapons and large boxes which he could not open, but were marked with the SS runes (he remembers this as he knew he better not touch those in case troops returned). He remembered paintings and statues that were secured with wooden frames. These were located not in the general cellar, but an adjacent room which had been covered with a book shelf in order to look hidden. I believe we managed to find this room 55 years later as it was a small door way easily covered by a bookshelf, in one were to try and hide it. There was also a chapel in the castle that was full of large framed and smaller art work.
By the way, he found no food but in error of his young age returned home with several rifles which his mother threw into the lake on the schuettdorf side of the lake. Not the things you want to be found in your house by liberating forces!
In the mid 2000s a gold cross was found in Thumersbach, with the last recorded location of which being at Fishhorn. It would appear some people did indeed open the SS marked boxes after all.
What is of note is that the castle has been in the same family for decades and the care taker knew a lot about its history. What we know for sure is that any treasure that was kept there was unlikely to be buried or hidden but kept in the castle. Between the looted gold being dropped off, the SS leaving the castle (before re occupying it a day later with the retreating SS division through Waldemar Fegelein) and the Americans arriving there was little more than 1 day to move it on. Thinking logically, if the room was that important to the regime it would have been loaded onto a train and moved out of the area along with the rest of the gold still at fish horn and not buried. If it was buried, why was the rest of the inventory not buried with it?
Im still in touch with some of my old friends, some of whom are quite interested in the local history surrounding the bernstein zimmer. One of them brings up a valid point in that if the room does still exist ( ie, not burned or destroyed during the end of the war) why would it have transported by truck. This is a large room with a lot of panels. The only feasible method of transport would have been by train and therefore is likely to have travelled on to Tirol or Kaernten, where ever those transports went. Personally i have the feeling that it was indeed found at the end of the war, and now sits in a warehouse somewhere overseas and the people who found it did not know what it was.
In summary, from the personal experiences Ive had in that castle along with talking to people who know the local history well through personal experiences, I personally do not believe that the room is anywhere in the area.