What connector have you got? If you're talking about the yellow 3.5mm digital jack on the back then yes, this will do 4 channels. It is just a stereo jack (like headphones) but each channel transmits a digital signal (which is also stereo), hence you get four channels.
Same with RCA out's. If there's two of them you've got 4 channels, if there's just the one then you've only got 2 channels.
5.1 is done on a single RCA using AC3 decoding as opposed to PCM which is what all the above is about. AC3 puts 5 channels of sound onto one connector. The sub is worked out by the decoder (I think?)
Seb