Probably best if you got a 4 channel amp. You can bridge two cahnnels to power the sub and then the two remaining channels powering the 6x9's. If you got a 2 channel amp you could run it in tri-mode (if the amp is tri-mode capable) whereby you run the 6x9's off the 2 channels and then use the same 2 channels bridged to runn the sub, this is not advisable as you have to use external high pass filters and an external low pass filter.
Matt
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