I talked with a friend of mine yesterday that is a authorized Garmin dealer. I asked him about the Service Bulletins I have been receiving about 430/530 Operating System upgrades. He said if you are interfacing your 430/530 to experimental avionics, DO NOT HAVE THE OPERATING SYSTEM UPGRADES INSTALLED. He said these updates are taking away the ability to communicate with the experimental avionics and once you install it, you cannot go back to the previous operating system. I guess Garmin is doing this to push their avionics that they are now making for experimentals. Also, if you are purchasing a used 430/530 and want to interface to experimental avionics, make sure these upgrades have not been installed. They have to be installed by an authorized Garmin dealer. The dealer has a list of what the upgrade is for and what it will do.