Those numbers, 192k, 384k etc are the audio bit rate, the k stands for kilobits per second. The encoding rate used during conversion should be the same or greater than the bitrate of the original audio. If it is less the audio will be more compressed than it was originally and may lose quality, although you'd probably have to lose quite a lot of bit rate before you notice. Choosing a different bit rate will not change the volume of the audio in the output file. Using a bit rate higher than the original will not make the output audio better quality; it will just make the output file bigger than it needs to be.
