Are you going to be playing multichannel Audio on this, or just watching movies?
If you are to play High Res material such as DVD-Audio or (cough) SACD, then you should definitely ensure that all 5 channels/speakers are as close to full range as you can manage, and all the same make & model.
This is also important for DTS Audio, and quite important for Dolby Digital encoded music discs.
For movies, it really isn't that important as long as it sounds good with a selection of discs.
What I do when speaker shopping is load up a bag with about a dozen discs - DVD-A, Music DVD, DVD-V, DTS-CD etc and compare.
