With lots of bikes the horn upgrade is on the short list, ours is so loud there’s not much interest in upgrades. Might find more info on a full wing forum if there’s nothing here.
I had an ST1300 with a wimpy horn prior to the B. The ST1300 forum was filled with horn threads, wondered why there weren't any horn upgrades on this site until I hit the button. I laughed out loud because it sounded ridiculous after the squeak that the ST1300 puts out.
My jacket sometimes catches the switch when stopped and getting something out of the left cubby, kind of embarrassing if I’m in a parking lot.
The issue with the ST was available current to run a louder horn. Check the circuit for the F6B horn, it may be enough for Stebel if that's your preference.