The Importance Of The Centre Speaker
Multi-channel music goes beyond the front stage to include surrounds and even an LFE channel. The exact amount of content sent to each channel varies from recording to recording and can be perceived as spacious and enveloping when mixed correctly. Film sound has always [post 1977] been mixed as multi-channel, and the number of channels has now expanded to 7.1 discrete channels [Blu-ray Disc]. However, because the centre speaker can be responsible for up to 90% of a motion picture's soundtrack, the quality of the speaker reproducing this channel needs to be as good as the L and R speakers.
My LCR Array
I use identical LCR speakers for two reasons –
1. Sounds do not change timbre as they pan across the stage.
2. I do not hear an audio quality change when switching from 2ch to MC program.
Whilst centre speakers can be bought individually, it is difficult to find a store that will spit a pair of "main" speakers so that you can have three identical LCR speakers. The solution is to therefore work out a budget for speakers and find the best centre speaker [that you both like and can afford] and buy three. As I am also a fan of bass management, I also recommend including a subwoofer in that system.
Mark