How to correctly play back Dolby Stereo movies?

[Menteith]

Ok, so let me start with the pre-amble that I was always under the (false) impression that Dolby Stereo just meant that - a 2.0 Stereo channel sound.

Now, I coincidentally found out in one of the threads on these boards that Dolby Stereo actually means 4.0 channel surround sound.

This means one thing - that I have been playing back all of my hundreds of blu-rays wrong. I always put my receiver to 'Stereo playback' for all these 80s movies, which resulted in sound coming out from L and R and the subwoofer.

What is actually the correct way to play this back? Which mode should one set up on the receiver for a dolby stereo movie (in my case a Denon AVR-X1200W)?

My assumption is that the mode should be set to "Dolby Surround", but I just wanted to make sure. There are other modes as well, which could make sense, e.g. "Direct/Pure Direct (multi-channel)" or "Matrix".

That's really a pain, why can't these systems just select the appropriate playback method by themselves?