I'd have to disagree. Look up the Harman white papers, Toole talks about how stereo is flawed. You can never get a proper center image from stereo. Secondly, 60-80% of the soundtrack, including effects, is mixed into the center channel. Official cinema specifications call for all speakers to handle full bandwidth sound with the dynamic range capability to reach 105dB. Most don't listen that loud at home, so we don't necessarily need that much headroom, but a good majority of wimpy speakers, as are most often employed as surrounds, simply cannot cleanly reproduce even 90dB (-15dbfs) at the listening position.
Discrete multichannel sound has made surrounds just as active as the fronts, with full range, and full dynamic range effects frequently sent to them, even with dialogue heavy movies, surrounds are utilized extensively for the music soundtrack.
Always buy the best you can afford, and do not skimp on any channel. Its fine to start with just the L/R speakers, but do not fool yourself into thinking you can cheap out on the center and surrounds. If your center and surrounds cannot cleanly reproduce the same SPL level with the same dynamic range as the lr then you have a compromised system and you most definitely will miss out. I would definitely buy a center before surrounds. You just can't get proper imaging with stereo, even in the sweet spot.
Onkyos theater dimensional DSP actually does a good job at giving you the illusion of surrounds with only 3 channels. Might use that until you can add in surrounds.
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