One set of RCA's will be all you need for the 2 channel. But if you plan on running 4 channel in the future, I'd go ahead and save yourself the headache and run another set since you're already tearing everything apart to run the 1 set. If you are planning on amplifying all four speakers, I would really recommend just waiting and getting a 4 channel. You dont want to buy 2 amps to do a job 1 amp can do because you are now splitting your main power wire 3 ways. Just for reference....a 2 gauge wire splits into 2-4gauge wires and 4-8gauge wires. A 4 gauge wire splits into 2-8gauge wires....and so on.
