Thanks for your info.
Airport Express definitely can join any network and use as a Wifi - cable bridge.
But I wonder if AirPort Extreme can only work as a bridge on an Apple network.
My set up uses multiple Airport devices for total coverage of my home for Apple and Windows desktops, my PS3, AppleTV 3, 2 iPads (1st gens), an iPad mini 2, 2 iPhone 5s, and a Galaxy Note 4. Also iPhone 3GS, 1st gen Kindle Fire tablet, a Nintendo 2DS...etc
1. Airport extreme 802.11ac connected to the modem and broadcasting 5Ghz and 2.4Ghz with my 80G PHAT PS3 and 3rd gen AppleTV connected directly via ethernet
2. Airport extreme 802.11ac extending the 5GHz network (with a 2009 iMac, Dell AIO, and work phone connected via ethernet)
3. Airpot Extreme 802.11n extending the 2.4Ghz network with a CyberPowerPC connected directly to that via ethernet
4. Airport Express 802.11n connected to the network and connected to a stereo so that I can play my iTunes music on my computer and on the stereo across the house simultaneously. It's fun.
In addition I have the other devices listed connected to either the 2.4/5Ghz network depending on each device's capabilities and I have zero issues what so ever.
I am currently looking for a very reasonably priced airport express to use as access for a single location for a wireless printer.