Are you sure the receiver is in 7.1 mode? Check whose problem this is by disconnecting the digital audio from the Pioneer (leaving just the 6 channel analog hookup) and then swapping the front analog pair with the sides and then with the rear. This way if you hear the sound (any sound) from the fronts at all with the sides or backs of the DVD player connected to the front L/R on the receiver you would know that there is something with the receiver - mode perhaps.

Axiom Setup