i have an apple tv in 1 room,airport express in other,can they be wired through router to an nas to stream itunes?? to both either togethar or individually?

If I understand you correctly: Yes and also no.

Can you connect your NAS, Apple Tv and Airport Express all to a Router? Yes, as long as the router has enough network sockets.

Will your Nas talk directly to your Apple tv? No. Even with a NAS, the media has to stream to your Apple tv through iTunes. ie: a computer on the network needs to be open and running iTunes for the Apple Tv to work. I am doing this right now from my Synology NAS 😀

OR, you can Jailbreak your Apple TV (as long as it’s not the latest incarnation), which will allow it to stream media directly from the Nas.

Does that answer your question?

My Zyxel 221 has an iTunes server built in. Would that not do the job?

Nope. Likely it’s firefly or some such diet iTunes-a-like program. The Atv needs a full fat version of iTunes to be running. Its total crap, and people have been complaining about it to Apple for ages – hence the reason lots of people are jailbreaking their Apple Tvs.