Definitely start with the test tones on the receiver. Some receivers (I have a Yamaha that does this) have a microphone that you set in the seating area and it will perform the calculations for you - but I'm guessing you won't be that lucky. I'd suspect that a lot of your material is not going to come blasting out of the surround speakers. They are mostly used to give a feeling of "place" to things off screen. Also keep in mind that the placement for "rear" surrounds is not supposed to be much behind you. They are supposed to be to the left and right of the listener, and maybe very slightly behind (such as mounted on a wall to the left and right of a couch). Placing them several feet behind the listener is the result of a common misconception.

If you primarily watch broadcast sports - I'd suspect you would notice very very minimal surround effect. Unless they truly are pushing 5.1 through the HD signal for that particular program, you are generally talking about pro-logic matrix encoded sound there - so the effects will be less than 5.1 and the rear channels will not be discrete.