Stream all sounds from Mac to stereo

I did a search but did not find the thread I was looking for, as I seem to remember reading about my question a long time ago.

I would like to stream all the sound from my Mac to my stereo wirelessly. Specifically, I would like to stream the music from some videos I watch on YouTube.

I already have Airport Express with iTunes. I seem to remember there was a software solution available. Or, is that just my wishful thinking, as I am aware of hardware solutions.

I believe you are looking for AirFoil

AirFoil Website said:

Send any audio from your Mac to AirPort Express units, Apple TVs, iPhones and iPods Touch, and even other Macs and PCs, all in sync! Airfoil for Mac gives you your audio, all around the house.

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