If you are doing surround sound then you would need to use all the preamp outs with 5 channels of EQ and power amp. An additional channel of EQ could be for a powered subwoofer.
Connecting all your speakers to the front pre out would only give you stereo and 2 channels of EQ can't be used to adjust for different speakers.
EQ isn't a substitute for good speakers and if used incorrectly could damage the speakers.