Again it has nothing to do with Apple TV. It happens on every HDMI connected audio source.
This is the type of troubleshooting you will want to actually test, and not just say.
Maybe, the AppleTV is waking up periodically. This wake up causes a HDMI-HDCP blurp with the receiver and television that causes audio to drop out.
You will want to unplug ALL sources from the receiver except one. I would go with the Blu-ray Disc player as that is the least likely culprit.
From there, you leave all sources unplugged completely, and you ensure that HDMI-CEC is turned off across ALL sources. Off in the receiver, off in the Blu-ray Disc player, and off in the TV. Then, test audio. If you get a dropout with the TV connected, then that's the most likely cause. Unplug the HDMI from the receiver for the TV and see if the issue goes away.
Now unplug the Blu-ray Disc player, and test with just the AppleTV. Same process. With the TV plugged in, and the TV unplugged. See if you have the issue in one case, and not in another.
Yes, as of right now, all signs point towards the TV as being the issue. When it wakes up briefly, the AV receiver is having some sort of handshake that it can't handle without dropping audio to the system. This is most likely HDCP related as even though the TV isn't powering on and I don't believe the receiver is switching sources at all, but the HDCP handshake can cause a brief dropout of your source until it is fully negotiated.
There is NO reason for this handshake to occur when the TV is in standby mode and that part of the chip should not be activated, and I don't know a good way to ensure that it is powered off and not acting stupid on you like this. But, your testing should not be by leaving everything plugged in as that leaves a lot of variables on the table. It likely is the TV, but it COULD be the AppleTV (even if that's not what is currently playing). It could be the Blu-ray Disc player (even if it is off!). But, unplug the world, then start with one thing at a time.
I do agree that this appears to be fully a TV thing. I'm not sure if there is any way in power settings to really bring things down to ground zero for waking up. You may want to consider completely disconnecting the TV from the Internet so there is no ability for apps to reach out, which may or may not impact things. Unless you are dependent on those apps, but with an Apple TV, you should be able to get by without them. At the very least, it's something else to test and try.