O.K. ... All Apple products (iTunes, iPods, etc.) can Play AAC music, but TiVo can not. Tivo wants to see MP3s. Similar, but apples and oranges to the hardware.
So, what you have to do is convert your AACs to MP3s... and here, iTunes on a Mac is different enough from iTunes on a PC that I'm not comfortable suggesting how. But if you do a Google search for ”convert aac to mp3 pc“ you'll find a bunch of options.
Just make sure you save your AAC originals... don't replace them with the converted MP3 files. You'll still want to use AACs on your iPod — they sound better.
(One more reason to use that AV cord and your iPod to listen to your music on good speakers, rather than as MP3s via your TiVo.)
One more option... if you have a DVD recorder in your PC, and a DVD player as part of your sound system, you can use iTunes to burn a DVD (in almost any format) and then play it back over your music system's DVD player. Or, just run a long audio cable down the hall from your computer to an AUX IN jack on your amplifier. (There are little transmitters/receivers that can do this wirelessly.)
Should your home be wired for Wi-Fi, there are a whole bunch of additional options.