How can I use AirPlay from a wireless device while in 'Join a network' mode with an Ethernet client?

Question

I just got the brand new Airport Express (simultaneous dual-band 802.11n) and I'm trying to set it up to join an existing working wireless network that I have in my house, and to drive my home stereo amplifier and have my desktop hooked up via the wired Ethernet port on the Airport Express.  Here's how I set it up:
-Wireless mode is 'Join a wireless network'
-Wireless Network Name: <my home network>
--Allow Ethernet clients is checked
-Internet is configured via DHCP (it gets a valid DHCP lease and IP address on my subnet)
-AirPlay is enabled
-The audio out from the Airport Express is connected to my amplifier via an optical digital cable.
If I leave it set up just as described above, I can select the Airport device from iTunes on my MacBook Pro and play music directly to the speakers.  Perfect.
The problem comes when I go to plug in my desktop to the wired Ethernet port on the Airport Express.  As soon as I plug in the Ethernet, AirPlay stops working on the laptop.  Even if iTunes is in the middle of playing a track, the track will stop when the Ethernet cable is plugged in (with a device on the other end).  Doesn't matter which of the two Ethernet ports I use.  My desktop is able to use the internet while plugged in to the Airport Express, but iTunes on the laptop is no longer able to connect to the Airport Express to use AirPlay.
I've found that if instead of plugging my desktop into the Airport Express's wired ethernet, I plug in the laptop, then iTunes on the laptop is able to use AirPlay -- but then no other devices on the network are able to use AirPlay.
It appears that as soon as I plug in a wired Ethernet device to the Airport Express it only "listens" to AirPlay connections from devices connected to that wired interface.  But this is the opposite of what I want.  I want it to listen to AirPlay connections from wireless devices connected to the same network as the Airport Express.  Is this possible?  Is there some hidden setting I have to enable?
Thanks!

Answer 1

Hi Hreb,
I can find nothing wrong with your configuration, but I was curious if there were something illegal about having an Express "join" a wireless network, and still have AirPlay enabled for wireless clients while simultaneously serving as a bridge to a wired one.
To address that uncertainty I implemented your proposed application with the preceding model AirPort Express, and determined it works as you would expect it to: I connected a wired-only PC to the Express, verified that it can connect to the Internet, and streamed Airtunes from a Mac to speakers connected to the Express. I think this is what you want, and it works with no surprises. I was also able to stream Airtunes from the PC connected to the Express as you did, but as you know only one device can stream to the Express at any one time.
I do not have a new simultaneous dual band Express to test though, so all I can conclude is that there may be a bug with the new one that is preventing you from accomplishing this.
Since it is new, I recommend you call Applecare on Monday and explain what you are trying to do. Explain it works with the older Express and you think this ability should remain unchanged with the new dual band model. It is likely they won't be able to help, and at best will offer to exchange it for another one, but if it is a bug as I suspect any replacement dual-band Express will behave the same way.
The important thing is to inform Apple and obtain a case number so that this problem will eventually get the attention of Engineering who might be able to address this with a future update.
Let me know what you find out. Thanks.