The Dolby Digital (or AC-3) audio standard allows for a number of full range audio channels (up to 5) and a LFE channel (subwoofer). The following configurations are possible.
1.0 Monaural without LFE
1.1 Monaural with LFE
2.0 Stereo without LFE
2.1 Stereo with LFE
3.0 Front L and R plus center or monaural surround without LFE
3.1 Front L and R plus center or monaural surround with LFE
4.0 Front L and R plus center and monaural surround or surround L and R without LFE
4.1 Front L and R plus center and monaural surround or surround L and R with LFE
5.0 Front L and R plus center and surround L and R without LFE
5.1 Front L and R plus center and surround L and R with LFE
Additionally the 2.0/2.1 format may be encoded for Dolby Pro Logic/Dolby Pro Logic II surround sound and the 5.0/5.1 format may be encoded with Dolby Digital Surround EX for a center surround channel.
Remove all but the AC3 5.1 and you will be OK.
NOTE: For those who don't agree with the preceding information, feel free to contact Ray Dolby at Dolby Labs, the source of this explanation. One of the brightest men in the industry and a genuinely nice guy.
"Thanks to the remote control I have the attention span of a gerbil." /.