neither....spend that money you wanted to buy the rear components with on a sub/box combo....bridge the rear channels to the sub and have a system that sounds 10x better then eitehr of your original plan....then again that's my $0.02 - do what you wish with it!!
Now IF you HAD to have one of the original options....get the co-ax's and hook them up to the RAF output on the Diamond Passives, then bridged said Alpine amp to run the whole front setup. This will attenuate the rear speakers and help to make things sound more natural