Airport express A1264 AirPlay

We cannot exactly promise you it will work on any and every third party router.

As Bob has explained the Express is still configured and accessed via the airport utility. And Airplay works via much the same mechanism. Some routers handle bonjour poorly and you might find the Express disappears occasionally from airport utility which will normally result in airplay also failing.

Ethernet is much preferred over wireless connections for that reason.

There are some settings that help.. static IP and set IPv6 to link local only.

Use short names, no spaces and pure alphanumerics. Not apple recommended names.. which break all those rules.

Passwords also same rules but 8-20 characters.

And use older firmware.. 7.6.9 is much more reliable cf 7.8.x even if the later firmware offers airplay 2 frankly it works poorly.

So I would say for 95% of installs following the above rules it will work fine.. and is clearly the best option for airplay with older amps that don't have it built in as most new models will.

No, it will work in a network either by ethernet to whatever router or as wireless client.

I am thinking of connecting one to my amp for airplay functionality.

This is very common way to use them.

No matter whether the Express connects to a network provided by an Apple router or a third party router, the Express needs to be configured using AirPort Utility on a Mac, PC, or iPhone / iPad.