The range of the receiver is from 4ohms to 16ohms (recommended) and typically receivers will go into thermal shut down if there is an issue with the ohm load. 8ohms is dead center of the range and is the most typical speaker on the market. So, you certainly are within the specifications of the receiver.
If it doens't work, then there is something else going on - like you didn't wire the red to the red and the black to the black on the 'LEFT' speaker. Or a wire is touching another wire causing it to shut down the amplification section to protect itself.
You want to double, triple, quadruple check your wiring against your owner's manual to make sure you have it hooked up properly and that there are no wire strands sticking out to cause a short.
