*.mp3 files and mp3 streams playing ridiculously low

After installing the KLite codec pack I realized that my mp3 files and mp3 audio streams from movie were playing very softly.

The same was the case for the ac3 files until I changed the decoder settings. I can't do the same for the Fraunhoffer decoder however since I can't figure out a way to access these settings.

Any recommendations?

reinstall the latest k-lite codec pack and select 'boost ac3 volume'

The only thing I can think of is the MP3 decoder that is included. But I never heard of volume problems with that. You could try to re-install with mp3 deselected. Then an other decoder (if present on your system) will be used.