Newbie question on 6.1 speakers - rear

Just building my HT, most of it still in boxes. So far, around a Yamaha receiver, I have a pair of Stratus Bronze for mains and (for now, till I find a C-6) a Paradigm LCR-450 center-channel.

My question for the rears: do people with 6.1 have three surrounds, or two surrounds and a center speaker? If it's the former (3 identical ones) looks like I have to buy 4 and park one in the closet...? If such is the case and WAF permitting, I hope to get three floor-standers.
Thanks folks.
As I understand it, 6.1 has 3 surrounds, left, right, and center. If one parks the L/R surrounds at the c. 4-o'clock and 8-o'clock positions as the ITU standard recommends, a surround-rear would serve to fill a hole in the (rear) middle.
Our best surround guy is slappy. maybe he can help.