Can't you sync .aac files to the zune? I've never tried but I thought that you could...
Sync audio files to your Zune device
You can use the Zune software to sync audio files together with your Zune device that comply with the following standards:
• Windows Media Audio (.wma)
You can use a bit rate up to 320 Kbps. For constant bit rate (CBR) and variable bit rate (VBR) files, you can use a bit rate up to 48-kilohertz (kHz) sample rate.
• MP3 (.mp3)
You can use a bit rate up to 320 Kbps. For CBR and VBR files, you can use a bit rate up to 48-kHz sample rate.
• Advanced audio coding (AAC) files such as .mp4, .m4a, .m4b, and .mov files
You can use a bit rate up to 320 Kbps. For Low Complexity (LC) files, you can use a bit rate up to 48-kHz sample rate.
From:
http://support.microsoft.com/kb/928191
Seems like even Microsoft thinks that you can. I know that there is no way to sync protected iTunes files, but I thought that you could sync ones ripped from cds.