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At a minimum, the receiver should amplify the signal from your PC so that it plays through your speakers. Whether or not it does anything more to "enhance" the sound from your PC depends on whether or not your receiver has any way to manipulate the sound such as tone controls or an equalizer.
Just to be clear: you have a cable running from your PC to the AUX input on your receiver. Is this a stereo cable? When you set the selector knob to AUX do you hear sounds from your PC through your speakers? If you do then your set up is working properly. You have a bass and treble control, as well as a balance knob. That's about all the "enhancement" your receiver can provide. Then again, that's pretty much what most people have.
I'm not sure if the OP wants some kind of enhancement or wants to eliminate any 'enhancements' in the audio.
Many receivers have a 'direct' mode which bypasses everything but the amplifier, cutting out all equalization and/or matrixing. If you are concerned about the sound from your PC being manipulated by the reciever in some way then you might want to check for a mode like this. Otherwise just set the bass/mid/treble controls to their neutral point (usually midway) and enjoy.
If you turn the receiver completely off and are still getting audio from the speakers... well... that's a new one.