Adding an additional siren or hooking up the horn with stock alarm system

The stock alarm siren of my 2nd gen CX-5 is weak. In planning to either

1. hook up the stock horns using relay by tapping directly at the stock siren (if its a siren. I haven't opened it up)

2. Add another siren (preferably) but do I just simply tap the 2 wires of the additional siren to the stock siren? I believe the stock siren is powered by a small PSU that is also a small amplifier. If so, won't the additional siren strain the power of the existing siren PSU system?

I'd go with hooking up horn