Hey Benolium...
I have that exact receiver in my main setup as my preamp... works great...
In order, you should be setting all your speakers to small, and start graphing your entire setup with test tones from about 100hz down... Try different settings, start at 80hz crossover and see how it graphs out...
If you have an major dips in the FR around where the subs are crossed over to the mains, you might want to change the crossover to a lower setting, and see if that makes any differences to smooth things out...
Looks like your speakers can play pretty low, but don't let that make you feel you can't crossover higher, at like 80hz.. let the graph be your guide. Your looking for a nice smooth response where all freq. are roughly the same db level.. little spikes and dips are ok, just not ones that move 10db...
If your really starting become a crack addict like you say, you can take another step further and download a program like
REW
or TrueRTA
http://www.trueaudio.com/
Also see Erics post here... already explained...
http://forums.audioholics.com/forums/showpost.php?p=342197&postcount=27
That will really give you an idea of how your room is reacting...
Good luck