Hello Pat,
You've perhaps read a number of my posts in the past concerning speaker positioning and the outcomes. Trust me when I say this, I've tried a bunch of different layouts!
The best answer I can give you for now based on the limited info I know about your set-up is it depends on how many audio channels you have, they type of sets you have (surround, wet, dry, etc.), how you are routing the audio and so on. I would say for starters, I would not place the large speakers to the rear, use them up front.
As I've reported in the past I've had very successful / the best results using a larger pair of speakers up front combined with smaller bookshelf / monitor sized speakers in a stacked arrangement on each side of the console with the stacks up considerably off the floor, in fact my top speakers are around 7' off the floor to give you an idea. I also have a total of 10 audio channels I'm using to divvy up in a very specific way which ranks I send to which speakers. We dubbed it some time back 'like sounding' pipe routing, or something to that effect. I can dig up the post when I did all this and put it here if you're interested.
Marc