FWIW, you do not want to use a sine wave signal to set peak limiters. You want a dynamic source. A quality digital recording of kick, snare and HH makes a good test signal. A speaker polarity test signal like the one The Cricket makes can work too. However, one thing I've noticed about the fast percussive attack of the cricket is that if your peak limiters aren't capable of being really fast, it can punch through the limiters pretty easily. So a more real world source might work better in that case. But that also says something else: not all processor are created equal when it comes to limiters. And it seems only the most expensive ones do a truly good job of limiting while still sounding good. XTA comes to mind. But it's also $5000+ for a 4x8. Worth every penny if you're serious about a good sounding processor and top notch limiters.
And as I've stated before, don't over-think this. If you're amps are sized such that they're close to the program power rating of your speakers, just set the peak limiters on the processor to keep the amps from clipping or at least clipping hard on peaks. If you want the 'tits' setup with hardcore rms and peak limiting, you shouldn't be looking at Behringer gear anyway. You'll need to plunk down some cash and get I-Tech amps. Or better yet, buy self powered boxes where all this stuff is figured out and implemented already. Going a piecemeal route with getting another external device to handle rms limiting and such is adding complexity that you really don't need to for a basic setup. Sure, you can do it, get the compressor/rms limiter, calculate the max rms voltage your speakers can handle, set the compressor according, etc. But it's really not necessary. There are tons of rigs out there running simple peak limiting and not blowing up. If you're going to be pushing your particular setup that hard, you should get more rig.
Greg