The people who know the most about the systems at your company are very likely the busiest. They don't have the time to prep a long presentation or write a lot of documentation.
How can you get them to spread the knowledge while not taking up too much of their valuable time?
Shift the work to the viewers
If you're interested in learning something about one of the systems at your company, list it on the infodump spreadsheet like so:
Start the votes column at one, because you're one person. Then try and get a few other people interested in learning about whatever topic you want to learn about. They should add votes if they're also interested.
Pick someone who knows a lot about this and put them in the presenter column. Once it hits a threshold (this will differ in places according to resources, demand, size of company, etc.), ask the presenter to present if they have an hour or so free.
Send out an invite to everyone who you think would be interested.
The format of an infodump session is simple. The presenter isn't really presenting anything. They might want to talk for a few minutes at the beginning to give a very broad overview of the topic, but that's it.
Then, the viewers ask questions. If the topic was HAProxy, for instance, a good starting question would be, "Could you walk us through a simple HAProxy setup with a health check?"
The presenter would then do that, live. If she has anything interesting to add or show the viewers, she could do that at any time.
It's essentially distilling down presentations to just Q&A, often the most interesting part of the presentation.
And record it if you can. There's a lot of great desktop video capture software nowadays, I'm sure you can find some. This will help avoid duplicating effort.
So the busiest people at your company don't have to do too much work. They field questions for an hour or so, and give live demos of cool stuff.
Communication is really tough. Infodump sessions should be just one of many tools you use to facilitate communication. Try it and let me know what you think.