Thanks for the input. I think ill pick up the JBL unit or the ion one (or both and return one) and see how it works.
One other question I have. I came across this one on Amazon. It claims 750 watts of power whereas the Ion is only 120 watts. Can someone help a noob like me understand what this means? Surely it doesn't give 5 times the output regardless of sound quality?
Edit to include link to the above mentioned unit:
https://www.amazon.com/dp/B01JKCRUCY?ref=ppx_pop_mob_ap_share
That unit is a junk subwoofer, and every spec. will be a whopping lie.
However let me set you straight.
What you are proposing is a total waste of money. In the open sound pressure level (how loud it is) decreases by the square of the distance from the speaker. Out in the open, there are no reflections, to reinforce the sound. So the straight square law will apply. So at 100 yards distance which is 300 ft, then at the back the sound will be will be 100,000 times quieter than 1 ft. away from the speaker. The precise calculation is a drop of 90,000 in sound pressure level intensity.
So lets take a ten yard distance from the speaker, 30 ft. Then the sound level at the 100 yard point will be just over 75,000 times quieter than the 10 yard distance.
So that is why both I and Hi-Fi are telling you that only a distributed audio system has any chance at all of doing what you want. Anything else is a total waste of money. In other words we are telling you that you have to get everyone in reasonable proximity to a speaker. The other thing that has to be engineered for is the delay in the sound from front to back, which has to be engineered for with delay lines. Sound travels at 1,100 ft/sec, which gives you 0.27 sec delay between the front and the back. That is a lot, and will really much things up, if not engineered for.
Not many members here have any experience with these type of installations. Hi-Fi and I do. So the only advice you need to take is from those of us who actually understand your engineering problem.