MediaMonkey's pretty good about converting from different formats.
MM provides a lot of flexibility on where to put the converted file, and you can set up rules for criteria on how to convert -- what bitrates to use, etc. You can level the volume during conversion if you like.
It doesn't have a built-in way to do this in a batch script if that's what you're looking for, though, but it does do the conversion in a background process so you could have multiple playlists being converted at the same time if you wish.