Well, just stop concerning yourself with 5hz. The content ain't there, and even if were, it can only realistically be reproduced by eight LMS-5400s + thousands of watts each, or a Thigpen Rotary.
I agree with whomever said to take these buttkickers out of your system and focus on improving the system as a whole... "get your priorities straight!"
Haha, I always seem to be both the person that makes things harder than they should be, and the person going against the grain all the time. But, I've had dreams of my butt shaking to movies for years, so my priorities are as straight as they can be.
Again, I may not have anything able to audibly reproduce 5 hz, but tactile reproduction is another story (no?). I admit not a whole lot of movies probably have anything down to 5 hz, but I'm sure I have a few in my library that do, and to me, it's worth it for those.
I've decided to just buy the buttkicker LFE kits. They are the same price as buying the buttkicker amps by themselves, so it's like getting the buttkickers for free. And the amps advertise a frequency response to 5 hz.
Then I'm going to use the (2) 2-channel crown amps to power the clark synthesis transducers which I'll have hooked up to the rest of the system. I have my mains crossover over at 40hz (they each have powered subwoofers attached to them) and everything else crossed over at 80 hz. So that's perfect specs for the crown amps.
And then I'll have 2 amp channels left over, which I'll use for the height channels to convert 9.2 to 11.2 with the Yamaha receiver.
So, it might not be everyone else's preferred solution, but I think I have a solution that fits my needs now.
...I think.