Unless you have a dsp, theres no way to run active and rears on your current head unit. Because once its in active mode, the rcas turn into low, mid and high, there is no rear.
If you really have to run rears,, check to see if you have proper impedance then you can wire the kicker and the alpines in series bridged to the mtx in 2 channel mode. Do the same with the new ppi 4 channel into 2 channel bridged with the kicker mid and silverflutes in series or both your 6x8s in series if you want to test it out with the rockfords as mids.
Series wiring will be 8 ohms since parallel will be 2 ohms and the amp bridged is only stable down to 4 ohms which means you'll still be seeing around 4 ohm load worth of power to each driver. Active will pretty much turn your setup into tweeters, mids and subs. No rears or fronts.
You can test around if you want but id personally sell it all and have two pairs of matching tweeters and two pairs of matching mids all setup in the configuration i specified because you can only tune for yourself and the rear might sound like **** because thats not the crossover point that particular driver likes. Also say good bye to any kind of halfway decent soundstage. Thats all down the shitter now. The other solution is to sell the excess and get a dayton dsp so you have 8 channels of control and you can actually do the setup right and have preset configurations for when your friends are with you and super SQ mode when you drive by yourself.
My actual two cents. Stick with the original plan leave the rears on head unit power. If you do the front stage correctly you should be able yo be heard several football fields away, there's no reason why it wont reach the back of your car.