It won't do a perfect match - Even the best REQ won't mix a LR mismatch (to use an extreme example)
However, almost all of the content during involving passages in multichannel is delivered through LCR
Perfectly Matched 7 or 9 speakers are great if one has unlimited pockets - For most mortals though, what do you think seems like a more likely comment from anyone wtching a movie on your setup?
A - "The dialogs on your setup are so natural and lifelike"
B - "oh man, that chopper that just flew past the screen sounded too bright when it went behind"