Wohw ...
Georg, I think I know what you are heading for, but the proposal is difficult to understand at this moment.
Let's first "state" (?) that Tinnitus is something in your head. Btw, this is not 100% sure for me, but at the same time people seem to suffer from it because of hearing damage. And besides that, it is said that the "beep" is caused by ear damage. This would make it not to be from your head.
Important ?
Maybe, but now I don't know enough about it.
Then :
Is a function possible, which filters out tinnitus frequencies measured by the audiologist?
... this is the part where I don't understand your proposal as of now. It is also why I said "it is from your head", or IOW / better : it springs from within yourself, and it is not a better/louder captured (environmental, like music) frequency. Or is it ?? If it is after all then my answer should be "yes, theoretically possible". If not, then possible "anti-sound" may help (same frequency emphasized but in opposite phase). Far sought ...
Now we are going to wait for our MD who knows all about this, or at least 1000 times more than I do. I hope he will respond.
Best regards,
Peter