I was wanting to suggest that Nextup offer an installer or a few installers for more common FOSS codecs.
Have the installer install some default baseline settings(tweakable by user)
codecs I would suggest would be
Flac: lossless audio compression, WAV quality without the size and no 4gb file size limmit)
Ogg Vorbis: Best lossy Audio codec per bitrate that has wide device support
Speex: gaining device support, and any device that has rockbox can play this format, its based on vorbis but optimized for voice data.
You can use the aoTuV or Lancer optimized encoders for vorbis(i can link them if you need them)
for speex and flac i can also link their current encoder versions.
They have multi options for encoder methods, dll and exe for example
these codecs are FREE no licence fees to use or support them unlike MP3.
Also a good option would be to check into RealAudio (.ra) as an option, a HUGE number of Asian/Chinese players support RA and all rockbox'd players support RA, and per filesize its quality for voice is amazing, 85mb for 6hrs of audio book(human read) no quality loss!!!