Airport Express WDS linksys WRT54G2

If you just need to stream AirTunes to your AirPort Express Base Station (AX), you only need to configure it as a wireless client to the Linksys router, however, if you also want to extend the Linksys's wireless network with the AX, then the WDS would, as you already know, would be appropriate.

Check out the following articles on how others have done this successfully with the Linksys:
o How to extend your Linksys WRT54G with AE
o Linksys WRT54G and WDS
o Using Airport Express as a range extender/repeater for Linksys Cable/DSL router WRT54G
o Extend a Linksys WRT54G network via AirPort Express

I want to do something very similar but I currently have my AX connected to my WRT54G2 via ethernet and then airtunes is running out of the AX. I would like to keep the ethernet connection and also have the AX extend my network, and continue streaming iTunes. Its wired for ethernet because its available and the signal is so much more reliable where is resides. That's why I don't want the AX connecting wirelessly to the WRT54G2. I just want it to also extend my wireless signal into the room.
Is this possible? I have an older AX g model but could get a new n model if thats what it takes.