After a little more research, I found the H-K radios absolutely will work in a pre-06 bike. There are 2 caveats though. One, if you want options programmed, the radio needs to be installed in an 06 or later biker, programmed, and reinstalled. The other is that Automatic Volume Control will not function. As long as you get past those 2 limitations there are no reasons why you can't use a Harmon Kardon in the older bikes. That being said, I would still prefer the RadioSound units. They are much more reliable. The H-K MUST be programmed before use. And not just programmed for options. Unprogrammed, the radio will play, but it will also make this CONTINUOUS loud beeping sound that is torture. And it cannot be programmed in a pre-06 bike. That means... you have to install it in an 06-later bike to be programmed, then remove and installed in the desired bike. Most people don't have two bikes that they can do this in.
By the way... the reverse is also true... The RadioSound radios will work in 06 and later models as well. The same caveat applies to the auto volume control. In an 06 and later installation though, you need to remove the wire for AVC.
The programing applies only if it is a New or unprogramed radio. If it is from a running bike that has already been programed, you will not need to reprogram it, unless it has it's memory wiped clean.
