If you are only using the digital input, definitely disable the 1070's auto-polling on that source. That will eliminate one variable from the test. Once you've done that, watch for two things: an audio delay, and a change in the front panel display to identify a signal acquisition. Any time the digital bitstream is interrupted and restarted, a receiver like the 1070 has to re-check the signal to make sure the format hasn't changed. This process takes a moment, during which time the receiver mutes itself to avoid unpleasant noise caused by mis-decoding the input. When the 1070 finishes the re-acquisition, it will display the format of the signal (DD 3/2.1 for Dolby 5.1, for example). That will indicate that the source device's digital output stopped and re-started.