As promised, the audio converter is here! It's in alpha stage right now which means command-line interface and mp3's only. Fortunately, for the click-happy among us there are batch scripts available for click-&-run use. Just download and place both the audio converter and batch script into a directory containing your mp3 files. Run the script and watch as the directory is (slowly) populated with wav files, correctly formatted for use in-game.
Advanced users can run hldjaconv.exe from the command-line for usage info. Adjustable options are rate, gain, and quality. If conversion is unbearably slow, adjust quality; if audio is too loud or crunchy, lower gain. Naturally, a full-fledged audio editor is still preferable for handling these finer details;
however, by virtue of its libraries, the HLDJ audio converter is arguably one of the highest quality converters available. The goal now is to integrate it and tweak the conversion process until it's fast enough to run on the fly.