You will need a minimum of a 2-way electronic crossover, that preferably can be set in the 2.5khz-5khz range. You would run the front output from the head unit to the crossover. Then the high output from the crossover to channels 1&2 on the amp, with your tweeters on channels 1&2. You would run the low output from the crossover to channels 3&4, with the mids on channels 3&4. The mids wont be getting a "rear" signal the will be getting a filtered "front" signal, not that it really matters. You will also need to use your amps high pass on channels 3&4, and this is all assuming you have a sub output from the head unit that you can run to channel 5.