Now, about those acoustics:

Someday you'll have a chance to deal with the acoustics, but in the meantime you need to do something with the speakers. Set up a speaker outdoors where there's no reverb, at eye level - maybe set it on a picnic table, right at the edge, best on grass rather than asphalt. Run a program into it. Spoken word is best. Stand in front of the speaker and listen for a bit. Then walk around the speaker in an arc toward one side. If you're lucky, there will be a rather definite point where the sound suddenly loses its "presence" or "immediacy." If the speaker has a large horn, this is likely to be the angle where the throat of the horn disappears from view. Take mental note of this angle.

Next, Walk the other direction and see if the angle is the same on the other side. It probably will be.

Then tip the speaker on its side and repeat the exercise, noting angles. Essentially, you're listening "above" and "below" the speaker, and this time the angles may well be different. Note these angles. Look at the horn and see if they correspond to the angles where the throat disappears.

What you're doing is establishing the coverage angle at mid and high frequencies.

Here's why this is important: "clarity" or "intelligibility" in a sound system depends more on avoiding echoes than on all other factors combined. The easy way to avoid echoes is to have no reflective surfaces - that is, to cover everything with acoustic tile. This option is not available to you, and I'd think twice about doing it anyway.

The other way is to place and aim the speakers so they cover the entire audience, but bounce as little sound as possible off the walls and ceiling. That's why you need to know their horizontal and vertical coverage angles. If you do this right, the improvement can be astonishing.

The worst possible thing you can do is put the speakers on stands, aimed horizontally at the back wall over people's heads. Raise them up, tilt them down. If you don't have mounting hardware that lets you do that, get some. If you hang them, use the best hardware and install about three times as many support cables as you think you need. A speaker falling on someone would close you down.

Another trick: music is one thing, speech another. It is useful to know that the speech sounds which carry information lie between 300Hz and 3kHz. If you want more clarity, don't turn up the treble. Turn up the midrange. A 3dB peak at 2.5kHz often works wonders. Your Yamaha with its scenes will come in handy here, allowing you to change from a music setup to a speech setup instantly.