Thoughts?
Scott
The best engineer in the world, given crappy mics and speakers, will have trouble with feedback and sound quality. I'd explain, very clearly, that better equipment is needed for better results. They've invested in a mixing desk which they probably consider quite expensive, and while I'm sure it's an improvement over whatever was there previously, it won't save you from awful speakers.
I'd suggest organising a brief demo, if it's convenient for you to do so. Take one of your speakers (preferably one that can go on a tripod), set it up, and play some spoken word through it. Ask your contact at the school to walk around and listen, paying attention to the clarity of the sound as they move around. Then, switch to their system and repeat.
I've done this before, and it's often an eye-opener for them. They assume speakers on the wall = everything's fine, and we know that's not always the case.
With regards to the RF, desk, etc, it depends. Will the Shure BLX do the job? Which capsules are on there? Are you happy running their desk?
Chris