zombie84 said:

... even a good mono source played through the centre channel will sound poor. The centre channel not only gives you bad audio spread, but it's a very weak speaker. Ideally you should be playing it back through at least one left and one right tower/bookshelf speaker. So, it's more that your equipment setting sucks balls. I don't know why they put the default to be centre-channel though, that's probably a consequence of compromsing for 5.1 defaults or something.

Centre channel speakers should be matched to the other speakers, and not be weaker.

You can listen to mono soundtracks through the left and right speakers (effectively creating a "phantom" centre) but this is not ideal - you need to be sat dead centre between the speakers. It's better to use a "real" centre if you have one.

1.0 tracks default to the centre speaker because that is the ideal way to hear them.