First Question: Why in the world would you power Alpine type R 6.5's with a Jensen amp? I just couldn't look past that one. I hope you realize that's a pretty bottom of the barrel amp powering some really nice speakers. As for 6x9's in the rear, I had some standard kenwoods back there, and they fit fine. You might even consider some 6x9 -> 5.25 adapters. Speakers are supposed to be round, not ovals. 5.25's will sound better and are cheaper. If you've got the money, do yourself a HUGE favor and get a decent 4 channel amp and you'll LOVE it.

Jason.