My new head unit supports 4-ohm to 8-ohm. I've replaced the old front speakers that were 4-ohm with newer Pioneer 4-ohm 50 watt rms speakers. They sound great. Got new 4-ohm 100 watt rms Kickers for the rear speakers. I just removed the old rear speakers and they were 8-ohm 20 watt speakers. Are the new 4-ohm speakers going to sound better and are they going to get more power?