I have the same receiver. I just tried playing an audio cd and switching sources on the receiver, but I couldn't hear any cross-talk between the sources. I even tried it a second time with the analog audio signal selected rather than the digital audio signal and still no cross-talk. Is there a possibility that he connected one of the dvd's audio outputs into a different source on the receiver? Perhaps he has a digital audio cable of some type going into the DVD digital input on the receiver, but mistakenly connected the analog audio connections to the TV/SAT source on the receiver.
If he has double checked his connections, than I might suggest at T2T did that the connections may be at fault...perhaps one analog rca cable is pulled loose and may be making contact with one of the other inputs on the back of the receiver.
Barring those scenarios, I'd be inclined to blame the receiver itself. However, knowing how heavy the 9300 is, I hope it's not a problem with the receiver...I don't ever want to have to move mine again!