I use the Nady 151VR-LT but am doing so using an amp. The Nady will, however drive a 15W horn, though personally I don't like the sound of a small horn. From having used the Nady by itself with a larger horn, I suspect your 25 W speaker may overwhelm it, causing distortion or clipping.
Even if this setup works, you'll likely find battery life on the receiver (horn side) will be limited to 45 minutes apiece when you use the wireless mic pre-amp as the only amp in your system. At that rate I'd buy a few rechargeable NiMH 9V transistor type batteries, and would plan on swapping them out at every new stand.
LionHo
