labels or manual?

most likly you have front,rear,sub and aux input. not two aux.

the one marked aux, is your input auxilary for audio in.

the other three are your outputs and seeing the two that are labeled, are your aux and front. then the two you have left are your rear and sub output.

to figure them out you will need to shut sub level down or off, then use fade to rear and the only one that should be putting out an audio signal is the rear. thats your rear. the other is your sub. now the if you cant turn or shut off the sub output completly in the hu options you should be able to adjust in some way and will be able to tell the difference between the rear and sub output if adjusted to a low freq. use a stereo amp in full range to run these test.

trail and error. good luck