Yeah traditionally most European ports were dubbed, but you still find examples of subtitles, especially in the case of quick imports and unpopular films. These days, it seems more common to subtitle a foreign film in Europe. I saw Due Date in a theatre in France last month, and even a silly film like that was subbed. But I guess if the German THX was the "premiere version" and it aired in the 80s (I am assuming this is a taped version of a very, very old broadcast in order to be called such a thing) then you are likely correct in assuming it was dubbed. But we should still acknowledge that this is an assumption though, since we don't actually know.