I tried setting my fronts to large and receiver crossover at 60hz. Bass seemed to cut in half. 80hz is definately the best with my Hsu STF 3. I had problems before finding a correct setting with a weaker sub, Polk 404. No such issue now. Even with an amp on my lows, set on small, sounds much better.
My thinking, correct me if I am wrong someone, is to use my Denon on the high's and midrange speakers, and power the 7" drivers with the amp for midbass, and my Hsu is for the low boomy bass. While it is true I may not be getting the most out of the power amp setting my fronts to small, it sounds better to my ears this way. I have considered scrapping the power amp all together and trying the Denon full range on the fronts to see if I hear any difference. My theory is the Denon is not being driven as hard the way I have it hooked up now.
I don't understand all this "efficiency" stuff and crossover points in my fronts. I may have this hooked up wrong, but to my ears, it sounds good.
Buckeye showed me something awhile back. If you want to see what those RTI 12's can really do, turn off the sub, set the crossover to it's lowest setting on the receiver, use the tone controls and EQ, crank up the bass and you will be amazed. Still not as good as using a sub, but you can get an idea what kind of bass those beasts push out.
Hope that helps. I still think I could have done better than the RTI12's for that kind of money, but I was new to HT and didn't know anything until I started reading this site. I do have to admit the brightness has been tamed a little with this amp and my hew house is carpeted compared to hardwood where i was before.