use airport extreme to play music and connect wireless but still use ethernet??????

here is my basic setup
MBP 2.2 has N built in and working

1.) Cable modem into wireless N router(forget brand I need this router b/c I have an access point in the house and have an xbox and other PC desktops hooked up to it)
2.) ethernet from back of router to airport station w/ airtunes(I use this to play music over my stereo wirelessly but I connect to the network setup by the router and have the airtunes "added" to my existing network)

here is what I want to be able to do.

connect to the apple airtunes to play music but be able to at the SAME time either directly plug the ethernet cable from the back of my router to my computer(for the fastest connection) or be connected wirelessly to either the apple airtunes station or my router dont care which.


here is what I have tried

to connect wireless to the apple air tunes and have air tunes connect to my network wirelessly to free up the ethernet cable so that I can connect that way when I am i have my computer on my desk.

I was able to connect to either the air tunes or my network never able to connect to both at the SAME time.

any ideas i know this may be very confusing? thanks