How do I connect my Apple TV so it shows video on my TV through my Denon AL24 receiver so that I can get the audio to go through my receiver?
Connecting HDMI cable to the HDMI jacks on the back of the receiver (DVR, DVD, etc.), but neither video or audio are working (yes, the receiver is set to DVR, DVD, etc.).
Is this receiver compatible with Apple TV?
Apple TV's Boxes are not compatible with most models of Home Theater receivers due to Firmware differences between the two devices. The workaround that is commonly used in the field is to connect the Apple TV box directly to the TV via an HDMI cable, and then run an Optical Cable from the Apple TV box's "Optical Digital" Output jack, to one of the Optical Inputs on the receiver to process the surround Sound. If you need further assistance let me know. If not, please do not forget to rate my answer.
Is it possible to update the firmware in my model AVR-3808CI so it is compatible with Apple Tv?
From what I understand, the Firmware updates available for your Denon will not help the Apple TV issue. What i would first do, is make sure you're using an HDMI V1.3 rated cable between Apple TV and the Denon, and additionally try other Inputs on the Denon to see if any work. There are Firmware update instructions for the Denon that you can "try", but I would be leary of trying them as I've seen issues with this Denon getting hung up on the update and needing to be sent back to Denon for service. If you click on the link below, and go to the first search result, there is a pdf file that gives you specific instructions on the update procedure. Again, the best solution aside from trying a new cable (V1.3) and another port on the Denon may be to connect directly to the TV and run an Optical Cable to the Denon.
I've been setting up Home Theater systems, and troubleshooting them for over 20 years.