1. Open SonicStage and select the "Tools" menu.
2. Click on "Convert Music Files" and select the audio files you want to convert.
3. In the "Output Format" drop-down menu, select "AAC".
4. Click on "Start Conversion" and wait for the conversion to complete.
Step 2: Transfer the converted files to iTunes
1. Connect your computer to your iTunes device.
2. Open iTunes and click on the "Device" icon.
3. Click on the "Music" tab and select the "Sync Music" checkbox.
4. Select the "Entire music library" or "Selected playlists, artists, albums, and genres" option.
5. Click on the "Sync" button and wait for the transfer to complete.
Note: If you have a large number of files, the transfer may take some time.