After having a 4-wheeler try to change lanes into me last week I went out and spent $150 for the Kuryakyn Hidden Horn. Basically, both trumpets mount behind the right bag on my '05 Ultra Classic. I also elected to keep the stock horn functional.

The time needed for the install was about an hour and a half as the supplied wiring was about twice as long as it needed to be and I trimmed the ends off a bit for a cleaner install. The new horn set is quite loud, and if at some point I decide that it needs 'yet more volume' I will add the Stebel horn in the location that the stock units currently occupies.

 

I've looked at those horns also, but if memory serves me right, they don't fit 09 and above.