The only mix to jpeg conversion we know of, is the export of old Microsoft PhotoDraw images (.mix) to JPEG format (.jpg, .jpeg), something which nowadays requires use of some graphics file converter.
You can also try some of the popular picture viewers with broad format support, such as XnView. It may not offer direct export to JPEG in this particular case, but perhaps offers export to other format which can then be saved as JPEG file via another conversion.