At Expressive Audio we love a 2.1 channel stereo system, and think no Home Cinema system is complete without a subwoofer to really bring the movie to life. They allow you to hear the .1 channel of the soundtrack that you'd otherwise be missing, and bring out the bass so your speakers can handle the frequencies they do best. We even wrote a blog about it here!
REL are well known in the HiFi industry for producing some of the best sub bass systems on the market, and this is largely down to the fact that they only design and build subwoofers...nothing else. So all their time, expertise and investment is solely focused on building the best sounding subwoofer possible!