Hi Katrin,
I currently can't activate SRBOX but was currently playing with device properties so it is fresh in my mind and might potentially be relevant.
If I activate "Keyboard" (Slide: Properties) there is an "Advanced" option which let's you select "Collection" where you could specify Response mode - alphanumeric only vs. all, and how Backspace is treated. Perhaps your SRBOX has similar options which could be modified?
Cheers, Yuliya