gutierrez,
levi might be right, the speakers might need to be broken in. i noticed that when my friend bought his new m72i's, they weren't as powerful nor as great sounding as they are today. but from your description, it seems that the sound is way weaker from what you would expect so it may still not be the answer to your problem.
have you tried other sources as they've suggested (fm radio, tv)? or maybe you can borrow a different set of speaker cables so that at least you can isolate the problem.
anyway, if iceman is coming over to test his receiver and speakers with yours, i think then we'll finally know the answer to this riddle.