What I did was cut the wires behind the head unit. I tied Front Left with Rear Left...Front Right with Rear Right. This means I can cut the Rear speaker wires and use these wires to connect to the amp (in the trunk). Then wired the Rear speakers to the amp too. Basically like this:

Front Right --><-- Rear Right --><-- Amp Front Right
Front Left --><-- Rear Left --><-- Amp Front Left

By doing this, and not removing the stock tweeters which was originally connected to the front speakers (with a capacitor as a crossover), the stock tweeters are still in the system. Is this correct?