ok - looks like the power handling of those speakers is 200 watts continuous (400 watts program); therefore, the amp you are using is probably a good match; and probably why you haven't blown any speakers.
The PR series look to be designed more for close field applications. Those speakers have a 90 x 40 horn in them - these are not really designed to "throw" sound, more like spread it around directly infront of the speaker. Something like a 60 x 40 horn would perform much better (even when using the same power).
I think what you have (speakers and amp) may be performing the best they can. You could scale back to 2 speakers each side (equates to more power per speaker), but there is a very good chance you would burn a speaker voice-coil.
Best to accept what you have and understand its limitations (which it looks like you have) or completely redo your entire setup (speakers, amps, generator, etc) to get more throw.