Have you ever noticed how an explanation with a whiteboard is often more clarifying than even the most meticulously designed chart or illustration? Even when there is no audience participation, a whiteboard explanation can be immensely more valuable than any professional presentation with the same information. It's certainly not because the chicken-scratch of the presenter on the whiteboard is more understandable. And it's not because the hand-drawn diagrams are more accurate or recognizable. So what is it about a whiteboard that makes the complex so understandable?
The key difference is that, with the whiteboard, you are there to witness it being drawn. Rather than having the entire finished product thrust upon your vision, you experience it incrementally, with an explanation of each piece as it is being drawn. This one monumental difference outweighs all of the graphic-design acumen one can muster. This fact can't be overstated. Well designed illustrations assist in comprehension. Audience participation also adds value. But when you are attempting to convey a complex idea, nothing comes close to the value of incremental illustrations.
So, does that mean that you must bring a whiteboard and marker with you to the next meeting with upper management? Of course not! The magic is not in the whiteboard itself. The magic is in its incremental nature. You can duplicate, and even improve upon, the process by adding fancy graphics, as long as you don't forget the fundamental principle of incrementalism. When creating a slideshow, include multiple slides for the same illustration. Have each slide in the set add a new detail to the illustration. The first slide in the set should have just one detail; only the last slide should include the complete illustration. That way, when you give the presentation, you can explain each detail in isolation before the addition of the next one.
Conversely, encourage your engineers to use whiteboards when discussing designs with each other. When they need to present something to you, encourage them to do it with a whiteboard. Make sure they don't draw it all out first before showing it to you. Make sure they draw it in your presence and explain it each step of the way. There's no reason for them to waste time preparing a fancy presentation when chicken scratch is just as good.