I have some games where comes pretty steam from the rear speakers! Mention should be there among others Fable 3 !!! Thus, (at least my) cable is not at fault are the rear speakers too quiet! Also, I've seen some movies where specifically very loud effects have come from the rear speakers!
Want when they are otherwise often quieter is the simple to the desired cheap reverb achieve the sound engineer in many movies, or music so! That you can use the rear speakers much better know, unfortunately only a few sound artists.
That's why I'm glad about getting notable exceptions where all-round sound really good use!
Examples in games that are noticed:
Fable 3 (Xbox360)
Red Dead Remtation (think is misspelled) (PS3)
GTA IV (PS3)
Anyway with Fable 3 you can very well remember that the rear speakers not at all have become silent (because the extension cord).
Hans Hartmann