I have a cooler stereo for floating the river. My current setup has 4 4 ohm 2 way speakers connected to a car stereo. I want to upgrade it and get rid of the car stereo and just use an MP3 player plugged directly into an amp. I purchased a 5 channel amp and an 8" dual coil subwoofer. The amp has a power rating for 2 ohm and a power rating for 4 ohm. Can I wire the 2 way speakers to the amp at 4 Ohms to get the lower power rating and wire the sub to the amp at 2 ohms to get the higher power rating for it or does it have to be 4 ohms to match the two way speakers?