Onkyo HT-S650 Plus a Sony SA-WM40 (1 Viewer)

I hooked up the Sony sub and calibrated it with the internal test tones in the receiver to 73 DB on the RS meter. The rest of the speakers are at 70 DB. I also calibrated the Onkyo sub to 73 DB. When I check the calibration with both subs hooked up they register 78 DB. They sound very good while playing Pearl Harbor.
Now for the questions.
1. Where should I have the crossover in the receiver set? (80,100,120)
It's very hard for me to tell which setting sounds better.
The crossover on the Sony is turned all the way up. The Onkyo does not have a control for crossover.
2. I haven't "stuffed" the Sony yet. Will stuffing it help the bass response? Will it hit harder?
3. Can I "stuff" the Onkyo Subwoofer? The amp is inside the enclosure.
4. I have lots of gain left on the sub level controls. Should I calibrate the subs higher than 73 DB each?
5.When listening at lower volume levels should I add some bass from the receiver?

The Sony sub by it's self thumps the Onkyo SKW-100 when both are set to the same level doing an A/B test.

I'm just trying to get the best out of my low buck system as money is very tight when you live in the middle of nowhere in West Virginia.

How do you like the SKW100 subwoofer? Onkyo's selling a reconditioned model on their site for only $59...

Is it worth it?