airplay error 15008 iTunes with Denon Receiver

Just about everything I found on the Internet says "power recycling" the Denon receiver solved the AirPlay issue for most folks. Not sure if it will help in your situation or not.

DLNA is not in play for AirPlay as they are two separate (but somewhat similar) technologies. You know that AirPlay is working since your other Denon receiver is not having an issue.

You can also try switching audio cables with these two units in case the cables may be the culprit. Even, simply, re-plugging in the same cables may be worth a try.

Which audio cable do you mean? There is just a TCP/IP connection, cable connection to the cable TV provider and a HDMI connection to the TV connected.

If the receiver is connected to the AirPort Express by Ethernet, you should try another known good Ethernet cable. Neither the cable provided by the TV provider nor the HDMI cable between the receiver and the TV should be an issue.

If the connection between the Express and Denon is wireless, I would still suspect that the issue is with the Denon and not the Express as AirPlay works with the other Denon receiver.

both receivers are connected via patch cable over a switch into the network, not via wireless. However, the network connection of the Denon works pretty well, all services (Internet connection, connection to DNLA Server and others) are working, so I suspect, the connection cannot be the issue.

Possibly, however, I would suggest that you switch the patch cable connection at the switch between the two receivers. This would either rule out the Ethernet patch cable or the Ethernet port on the switch.

One question: You are talking about AirPort, the issue I have is accessing in iTunes via AirPlay. Is this the same or something different?

By "AirPort" I am referring to one of the Apple routers. AirPort Extreme, AirPort Express, or the Time Capsule.

AirPlay, on the other hand, is not dependent on the router manufacturer, but is an Apple propriety IP protocol suite used for streaming audio/video. It would be somewhat analogous to DNLA. AirPlay, like the DNLA protocol, can be transmitted over either a wired or wireless network or some combination of both.

Both require:

1. A "server." For AirPlay this is typically iTunes, but is not limited to it only.
2. A network. This is identical to both.
3. A "player." For AirPlay, this can be an AirPort Express, Apple TV, or an AirPlay-Ready device, like your Denon receiver.

The AirPlay "server" must first identify an AirPlay "player" and establish a connection to it, before it can start streaming. So, either the server cannot "find" the problematic receiver, or it can find it but cannot stream to it for some reason or another.