How would adding a 3rd speaker change anything? The broadcasted signal is still a 2-channel audio, right? Is the amp just going to transform it to M/S and use mid channel for the center speaker?

Well actually what we mean is that some content is not in stereo and therefore you have a missing component.

You can always set your system to dolby sorround even though you dont have the speakers for it, but what will happen is that you will miss a Channel.

So lets say you are watching 5.1 content over 2 speakers and your amp does not break it down for you, you will be hearing the content of the people speaking weirdly low and all effects REALLY loud.

This is because your tv is trying to send you audio on a speaker you are laking and thus it swallows it. This makes the voices of characters sound further away and can be freaky :D

I see, thank for explaining. Yes if you have the option to receive more than 2 channels then I can see how that would give some flexibility. I didn’t realize that TV channels offer 5.1 (I don’t own a TV set).

Saying that if you are receiving a stereo signal - which I expect is the default option - then adding another speaker or changing the amp won’t make any difference, right? Or is there some amp processing technique that improves even a stereo signal?

Yes! but the "problem" here is that some services will send you sorround sound by default trying to get a 5.1 signal to speakers that dont exists.

Its quite a weird feeling if you figure out you did not connect the center speaker after a month, only to realize that "how you could have lived with yourself remains a mistery" :D