Finally got around to replacing that wimpy sounding "meep meep" horn with dual horns. The horns I used were 135db models. I used a low tone horn and a high tone horn. I got the horns from carparts.com for $16.00 for the two horns (contrary to my writeup below that says $31 as the $31 was for 4 horns). The 3 wire tap I got from Radio Shack for $3.99 for a 10 pack. The wire I got from Radio Shack a while ago.
I elected to remove the front bumper to do the horns. It is remotely possible that you could do this without removing the bumper, but you would have a heck of a time working from the ground looking up into the tight space that these horns occupy.
The car in the writeup is my 2009 Sport. Let me know if you have any questions or comments. In total, with taking all the photos and working slow and deliberate, it took me about 2 hours to do this. Without having to take the pics, it probably would have taken an hour or so.
EDIT - Forgot to mention, these horns are LOUD. Much louder than stock. They also have a deeper tone that sounds great and not at all like the "meep meep" sound that comes from the single stock horn