Are you sure this is EAST Berlin? The last GDR (Mitweida) concert by Joachim -- sans Rolf -- was in May 1966, he left the GDR through Vienna one week later. Rolf was a welcome guest from Hamburg (West Germany) before that time, but seeing that his seminal Solarius album on the GDR Amiga Jazz label (1964/5) was pretty much boycotted after Joachim went over, I can hardly imagine the two of them performing in East Berlin in 1966.
Leafing through some books, I see there was a "Jazz in der Kammer" (E-Berlin) concert by the Kühn brothers on 31 January 1966. Maybe this is it?
Do you have any more details on the personnel?