Matt, glad I could help. You should be able to adjust the LFE output on the receiver by 5-10 db, which hopefully will give you the flexibility you need.
I did not mean to besmirch the Fluance speakers. I apologize if it came out that way. I was concerned about you taking those measurements too literally relative to the crossover setting on the subwoofer. Like I said, you shouldn't even need to invoke the crossover on the sub if you are feeding it from the LFE output.
If you are dissatisfied with the surrounds, you might consider replacing them with the Axiom QS4 or QS8's. They are truly remarkable speakers, and would be a meaningful way for you to upgrade now while staying consistent with your future path.
Don't dismiss the Axiom speakers that are not their "top of the line"; many board regulars report great satisfaction with the M22, M3, M60 and other models. The M80 seems to require a fairly large room for best results, and can be somewhat finicky about placement. Axiom advisors have asserted that the timbre of the M60 is virtually identical to the M80, but that the M80 has greater power handling capability.
You are well-set on the sub, and would likely have a life-changing experience by changing to Axioms. Your receiver will have no trouble powering them, and needn't be replaced until you need more features or MUCH more power. As a matter of fact, I believe that Axioms are significantly more efficient than the Fluance speakers (if I am looking at the right model), so you would realize greater SPL capacity just by switching speakers and keeping your existing receiver.
So, go order up already! You won't be sorry!
At any rate, hang around the forums and give us the benefit of your experience.
