Maybe it would help if we head this off a little; perhaps others can reply with any other configuration tutorials:
1) You will need to read a lot. There is no shortcut here.
2) Read the manual Outlaw gave you
3) Read this AVS Audyssey setup guide
. Even if you don't have Audyssey as your room correction software, there are still some tips that might help so that you know what questions to ask. It also talks about setting up dual subs.
4) If you are a Denon user and still don't understand how your Denon receiver works, read batpig's guides and other info on Audyssey and Denons
5) Follow the recommendation (see the Audyssey guide) to get the sub channel(trim) level set by the receiver set in the -3db to +3db range by your room correction software. That might mean turning the gain (volume) knob on the sub down more than you think you need to and running Audyssey multiple times to get it right.
Anyone have a good, easy to read resource on sub placement to go with this?