I want to install an Alpine CDE-9872 into my 1988 Volvo 760 Turbo Wagon. The present head unit is a SONY with 7.7 ohm dash speakers and 4.5 ohm 2-way speakers in the front doors. No speakers in the rear doors at this time. I plan to run 7.7 ohm 2-way dash speakers, 4.5 ohm 2-way front door...