If you have "normal" (i.e., not "Elite") Everest 100, Everest 300, or Everest 700 headphones and have sound lagging behind video then you're in luck: I have located the elusive firmware update over on JBL's Japanese site. The site isn't in English but the firmware package itself is and includes English instructions.
Here's the link to the firmware:
http://support.harman-japan.co.jp/update/data/HID.zip
(updated link March, 2021 - thanks commenter rteng!)
For a Google-translated-into-English version of the web page, click here.
I was able to upgrade a set of Everest 300 headphones from firmware v1.1 to v3.1 with no issues (via USB connection to a Windows 7 PC). The update fixed the audio lag issue for me but your mileage may vary.
Cheers!