Li,
Glad you are finding it useful.
My original files are 24kbps. So can I use the iTune tech to do what you had instructed and go for 64kbps?
Yes. In the iTunes method, you need to set the bit rate and sample rate in preferences in advance. In the Import Settings, choose "MP3 Encoder" and then a "setting" of "Custom." This brings up a dialog where you can request a Bit Rate and Sample Rate. Save your settings. Then, any time you use "Create MP3 Version," you will get output with those settings.
Do a few files to start, make sure they sync properly, and when you are convinced that all is working well, do the rest that you need.
When you are done with this project, put the Import Settings back to normal, as the ones you will be using for your spoken-word files will be way too low for decent music quality.