Is two streams possible?

I may be attempting the impossible here, but....

If I am viewing a web page which I wish to mirror to my TV via my Apple TV box, I can do this easily.

However I also wish to turn down the sound on the TV and stream an iTunes playlist to my Stereo via an airport express.

Two different streams to two different devices.

I have been playing around with the send to multiple speakers option, on and off; and also the order in which I try to set up the two streams, but I only seem to be able to have one or the other.

Should it be possible to achieve this or am I simply attempting the impossible?

Many thanks,

David.