You mean multi-channel stereo? I wouldn't. I would just use a direct, or Dolby/DTS mode so it routes the appropriate content to each speaker.
Adding a subwoofer allows you to get the LFE track from movie soundtracks and it also allows you to cross the bookshelves and center over at a certain frequency so they aren't overdriven, which will allow you to play loudly, more cleanly, and will provide you with better overall bass response even at lower volumes.