Changing audio out to mp3

I am a simpleton with this type of software and I have what is, hopefully, a fairly simple question:
How can i modify the Panasonic Viera St50 profile in a way that would result in the output audio of transcoded files to be mp3? I have a soundbar connected to my tv through digital audio out, and right now any avi file that is transcoded leaves my soundbar saying it can't play the audio. I believe it will play mp3 audio and whatever the default audio is in an mp4 file as well (my tv does not require the mp4's transcoded to play properly and the audio always works).
Thanks for any help
How can i modify the Panasonic Viera St50 profile in a way that would result in the output audio of transcoded files to be mp3? I have a soundbar connected to my tv through digital audio out, and right now any avi file that is transcoded leaves my soundbar saying it can't play the audio. I believe it will play mp3 audio and whatever the default audio is in an mp4 file as well (my tv does not require the mp4's transcoded to play properly and the audio always works).
Thanks for any help