Apple TV won't play 5.1 sound ONLY on ripped movies

I have AppleTV 2nd generation connected to my AVR and it outputs 5.1 sound when playing certain Netflix content.

However, it won't play 5.1 sound on my ripped (owned) movies when streaming from my computer, only plays stereo. I've changed the settings to "Digital" in the ATV but that didn't work either. I've tried holding down the select button to change audio tracks from stereo to digital but it doesn't give me that option (gives me options for subtitles and to play on other ATV/computer speakers.) Have tried both with the HDMI connector and with an optical digital cable, same results.

I'm pretty sure my movies are properly ripped, I used Magic DVD ripper. If I do a "get info" on one of the .mp4 movie files it shows "encoding: mp4, aac" and "audio channels: 2" (I assume that means 1 channel is stereo and 1 channel is the 5.1.)

Any suggestions on how to get my ripped movies to play 5.1 on my ATV?

Thanks,

Kevin