Well they're a 2.1 sound system. They're not designed to fill house with loud music. I have them too and they sound great in the room they're in, but fade away quite a bit as you walk out of the room. They're just not designed to be something like a surround sound type sound that would fill multiple rooms with crisp, loud music.
The only thing I may suggest is, in iTunes, do you have the Preamp turned up? Most likely you won't be able to turn it up all the way depending on the type of music you listen to, but if you turn it up about half way you'll get louder music out of the sticks.