Hi pdermody,
Does the 3803 have a headphone output? If so, turn off the M80s and listen there. Usually, the headphone drive is simply padded down from the stereo amp output, so if the distortion was present there, the M80s would not be at fault.
There's an outside chance that the CD/DVD player line-level output might be overdriving and overloading the preamp input section of the 3803. Although the fixed output level of CD players is supposed to be standardized at about 2 volts, some deliver a lot more, which can overload the input sections and cause distortion. If you also have a variable output on the CD player, try reducing it to see if the audio anomalies disappear.
Regards,
