Drive two speakers from one amp?

Hey guys.
I have a Bryston 9b ST (5 channel amplifier) and I am not real happy with my current center channel speaker. I have a pair of SF Cremonas for my left and right channels and a pair of SF Grand pianos for the real. The center is the SF solo and it seems the weak link in all of this. I have a chance for a pair of SF Concertos that I could use for the center and was planning on running both off of the same channel on the bryston but dont want to blow out the amp. I pretty sure the SFs are 8 ohm speakers and if my understanding of impedance is correct that wiring two speakers in parallel would be equivalent of driving a single 4 ohm speaker. Anyone think I might have a problem with this.
Thanks in advance for your advice.
Why use just one and avoid impedance and imaging issues?

Why not hook them up in series and double the impedance?
Also keep in mind impedance is not a constant thing-it varies with freq. So if nominal 8 Ohms, it could be a good deal lower than that at spots in the frequency response. So in parallel it could be a good lower than 4. This will heat your amp up and drive it harder. Yogiboy is exactly right, series would be better, not to stress the amp.

BUT Kal's answer above is the right one I think, as now two speakers right next to each other will combine and change dispersion patterns significantly from a single speaker alone. Two wide horiz dispersion speakers side by side (right next to each) become less wide. Two speakers on top of each become less vertical. Think speaker columns-as you increase the driver count vertically you cut the vertical dispersion and widen the horizontal. This works great to shorten "throw" and keep it wide (anyone ever see those gigantic speaker stacks Grateful Dead used to use?). Shorter throw might keep audio off the back wall of an arena, but at home if you stack two identical speakers on top of each other you may notice the speakers don't sound at all the same 8 feet away as they do at 2 feet away.

Also if the speaker is designed to be upright, turning it on its side will rotate the dispersion pattern 90 degrees. What was a wide horizontal/narrower vertical dispersion pattern (good) may not be a wide vertical pattern and narrow horizontal (bad for home hi fi).

Sometimes more is not better!
You could always wire the speakers in series, as has been suggested.
However, you may want to face one backwards than experiment with bi / di pole phasing.
Hey Thanks for all the advice. I am going to abandon the idea since I dont want to overtax the amp.(I know that wouldnt happen in series but still) The only reason for the idea is that i had a pair of floor standers that I could use for the center but didnt want one right in the middle (it would block the TV, I know I should have a dedicated listening room). I will look for a really good center and sell the floor standers. Thanks again. I knew I could get good advice and answers from the knowledgable folks on Audiogon.