Yes, you can use the AirPort Express Base Station (AX) without an Internet connection for iTunes streaming. The AX would not get a Public IP address, but it would have a Private IP address of 10.0.1.1 ... and it would be providing wireless clients connected to it with Private IP addresses in the 10.0.1.2 - 10.0.1.200 range.
Note: The following instructions are intended for the 5.x version of the AirPort Utility.
AirPort Utility > Select the AX > Manual Setup > AirPort > Wireless
- Wireless Mode: Create a wireless network
- Wireless Network Name: <enter a desired Network Name or SSID>
- Radio Mode: <leave the default or select a desired radio mode>
- Channel: Automatic
- Wireless Security: <select the desired wireless security type>
Internet > Internet Connection
- Connect Using: Ethernet
- Connection Sharing: Distribute a range of IP addresses
Internet > TCP/IP
- Configure IPv4: Manually
- IP Address: 10.0.1.1
- Subnet Mask: 255.255.255.0
- Router Address: 10.0.1.1
- DNS Server(s): <leave blank>
- Domain Name: <leave blank>
Internet > DHCP
- DHCP Beginning Address: <leave default or change to a desired starting address>
- DHCP Ending Address: <leave default or change to a desired ending address>
Music
- Enable AirPlay (checked>
- iTunes Speaker Name: <leave default or enter a desired speaker name>
Your AX may report the following errors: 1) Configuration of WAN, 2) SNMP over WAN, and 3) Double NAT. These can all be safely ignored to stop the AX's status light from flashing amber in this configuration.