Rendering audio tracks to WAV files takes a long time

I'm rendering out separate 5.1 audio to WAV files (separate L, R, C, LFE, Ls, Rs files). This is a 10 minute short film and it taking 1 minute 15 seconds per track, and it has to do each one individually. I don't understand why it's taking so long. I can output the same audio tracks for a feature in about 5 minutes. This is a 10 minute short and it takes about 8 minutes. Why?

Also, there's no way to render the audio files without text being automatically added to the beginning of the custom filename I selected. For example, I'm getting "A6-0001_" at the beginning. Why can't we tell it not to add text to the beginning of the filename?