Sound quality?

[glenn22]

Ok, first of all I know almost nothing about sound on movies... video yes, sound no. Here is my issue:

I bought an optical cable to connect my satellite reciever to my a/v reciever. I was watching a movie on an HD channel that included dolby digital 5.1 sound. I found that the sound was very clear but the dialog (talking) all came from the center channel and sounded very tinny..... is that normal? The surrounds effects and background noises were awesome, but it seemed to be ruined by the tinny sounding voices. Could this be just a not-so-great center channel speaker?

Oh and also, is optical the best connection for sound?