What will happen is you will be running (assuming you are using all 8 ohm speakers) 4 ohms in the C and 8 in the L & R. This probably isn't a good idea since you will get more power to the C than the L and R . Why not just use one of the old floorstanders. As far as the sub, freq. that low can't be localized, so it shouldn't matter where the thing sits. You could also use one of the bookselves as a C. Hopefully all your drivers are the same size.