Basically the Beam represents the front soundstage. So you cannot do what you are proposing. Here are your options: 1. Do not use a Beam and simply use an Amp for the front speakers. Adding a 2nd Amp for the rear speakers. 2. Use a Beam/Arc for the front speakers. Abandon the other front speakers. Add an Amp for the rears. 3. Go with option 2. but use the same rear speaker Amp and connect that to all 4 speakers that are in-ceiling/wall. This would only work if the front speakers are in-ceiling speakers vs. in-wall. If they are true front left/right speakers this won't work. If they are in-ceiling and all 8 ohm speakers, you could try this.
"Just when I thought you couldn't possibly be any dumber, you go and do something like this... and totally redeem yourself!"