Can you return the amps??
a:I would get one solid 4 channel to run the 8 speakers at 2 ohm stereo and one amp for the sub.
b: Run one 4 channel amp for all the interior speakers and one 2 channel dedicated amp for the tower speakers and a 2 channel for the sub
I do belive Pac makes "splitter" for your needs. Or just get y adapters for the 4 channel amp.