there is a couple of possibilities, although they may or may not apply to your situation, 1, depending on your tv, and how you have the audio connected to your receiver for regular tv, if it is connected by way of audio outs from the tv to the audio in on the receiver, then its a matter of if your tv has any sort of volume leveling (usually called dynamic compression, late night mode or a marketing term that follows suit) the downside to that is, if you happen to be watching a movie on regular tv (not a dvd) then you are going to lose the dynamics of the movie as well, the hair raising crescendos in the orchestra score or the subtle effects of a child whispering, they will all be roughly the same volume. but depending on how much you watch normal tv to watch a movie you should be alright
2. the other way has to do with the same thing, but only if you are using digital cable or another digital source to watch tv. then you would want to look for the dolby digital compression on your receiver and set it to high. correct me if i am wrong but that will only normalize the volume of the dolby digital signal, and if the tv program, or even just the commercials arent in dolby digital then it would defeat the purpose...
just my thoughts...