You can use either, or both the airport express or the tivo to play your music on the stereo. There are pro's and con's of course, but in general the airport express with airtunes gets my vote.
Airport Express with Airtunes
The Airport Express (AEX) recieves music streamed to it from iTunes running on a Mac or PC on the network. The advantage here is you get to use iTunes to play the music, which means access to all of your playlists. It's far more flexible than the Tivo. The drawback is that whichever mac you use to play the music on (and send it to the AEX) cannot simultaneously play music on the computer either. However you may be able to do this by logging in as a different user.
Tivo with Tivo Desktop
Tivo supplies server software which runs on either Mac or PC. This software runs in the background and serves up your music and photos independent of iTunes. The advantage is that one person can play what ever they want on the stereo by selecting from the Tivo, while someone else can play whatever they want on the computer. Also Tivo Desktop will serve up your photos which AEX will not. The downside is that navigating and searching your music via the Tivo is cumbersome. The Tivo may not be able to play anything but MP3 files. So if you have any music encoded with the default iTunes AC3 encoder, or music purchased from iTunes Music Store, that will not play via the Tivo.
For these reasons I would suggest using the AEX to play music and install the Tivo Desktop to serve your photos (as well as music), and you will have the best of both.
I just received a TiVo for Christmas. I also received an Apple Airport Express. I would like to get my music from my Mac (iTunes) to my home stereo, which is in another room. I presently have a regular Airport network in the house. I thought I would use the Airport Express to achieve the hook up to the stereo, but the packaging on the TiVo says it can do the same thing. I don't want to open these boxes until I know what I need. Any ideas?

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