Glad the install went well and the radio works. How the Automatic Volume Control works without any input after cutting the speed signal wire (pin #9) is a mystery. In the pre-'06 bikes, that white/green wire was a signal from the Vehicle Speed Sensor. In the '06 and newer models, that pin is used for the serial data bus which is also used by the speed and tach. With no pin #9 connection to the radio, it's unclear how the radio would know what the bike's speed is in order to adjust the volume.
Perhaps your buddy who knows the HK headunit can solve the mystery. I'm not much of a "why" person - if something works well, I seldom need to know why it does. In this case, I'm about to install an HK headunit in my '04 EG (99% because I want the cleanest CB installation) and anticipated removing the white/green speed signal wire from the AMP connector that plugs into the back of the HK radio, and replacing it by tapping the serial bus wire to preserve the AVC function.
Let me know what your bud has to say. Thanks.
Carl