Updated: May 6
Extreme high density is sometimes difficult to configure the WLAN, no matter what the brand of WLAN. Here are some ideas that may help you there are too many people on at the same time.
Turn off the 2.4 Gig radio
Set the 5 Gig radio at lower power to only cover area closest to AP, but ensure overlapping 10% coverage with the other access points.
If you can, turn off authentication, have an open network.
Turn off advertising and splash pages
Turn off automatic channel selection
Turn off automatic power settings
Physically survey area with 5 Gig radios for minimum power for each area before two days before the start
During physical survey make sure all areas have at least -70dBm reading
Depending on the density of clients you should consider manning the cloud controls to handle any problems that may happen during the event.
Remember to temporarily add more bandwidth from your ISP and make sure you edge switches and intermediate switches and handle the extra load.