Hi David,
The panels are removed/accessed as follows:
First you need to lay the speaker down on its side or on its back supported with a stool or box to support the top section. Use a soft blow hammer and tap upward on the bottom of the wood rail. It will relieve the tension on the pin and grove system. Do this to both sides. Make sure to not let the panel flop out.
Once you have the panel back in it's proper position, you may want to do this update:
http://www.martinloganowners.com/forum/showthread.php?t=3433&highlight=remove+panel
Good luck,
Mark