First of all congratulations on getting a new bike
this is my personal request not to go for so massive horns, as these r really harmful to the hearing ability, specially pressure horns.
Han there is a safe way to increase the volume of existing horn, go to a good electrician and ask him to install KITOUT on this horn. that part will not let horn use battery and will increase volume of your existing horn by 20 to 30 %.
If you could please refrain from using high pitch horns it will be a personal favour.
Thanks very much