I second that...
WaveGain would probably be the easiest solution, because you'd only have to do it once to permanently alter the gain of the WAV file from which all other encoded variations of the file will come. The only downside (I can think of) is that WaveGain is lossy, in the sense that using it eliminates any bits in the WAV file representing sound pushed below the noise floor when a gain adjustment is applied. But I've never heard of anyone being able to tell the difference in sound quality of a "reasonably" adjusted file (about 4dB to 7dB). Exceptions would occur if the file is adjusted *way* too steeply, such as turning down a file down by 50dB, then back up...clearly anything except fairly loud passages would be gone. If I regularly used formats other than MP3, then I'd use WaveGain myself.
Specifically for Ogg you can use VorbisGain, which you can find at the
Rarewares - Ogg Vorbis Software section. I don't know if it's gain adjustment is lossless or lossy, though.
As for MPC, AAC or WMA, I don't know. A forum search (if you haven't already tried one) might turn up more info, as well.