When I actually noticed that the manufacturer's instruction page didn't mention the bracket issue was later, when I was wondering where to stick the crossovers. That's when I noticed how generic the install page was. All it said (basically) was "stick them where they'll fit."
Trouble is, at least on our bikes, there's not a lot of places inside the fairing where you can stick them down. Just not a lot of unoccupied flat surface. This is even worse if you happen to be using HawgWired's other amplifier kit as the area on top of the radio is already occupied.
Finally after 15 minutes of poking, sticking, cussing and wondering I settled on sticking the crossovers up above the speakers. The speaker mounts have a decent surface area up there that actually works ok. It could be better. But it's ok. No interference came from the crossovers to either of the antenna mounted inside the fairing (XM or AM/FM/WB). So all is good (enough).
After shoe horning the HK radio, XM module, that systems big harness, the amp kit and now this stuff inside there, however, I don't think anything else is getting stuck inside the fairing.