Tag & Rename allows you to pick a starting number when autonumbering the files.
Could be handy for all the audio books I rip, but I use another method: rip each CD with the CD# in the Album tag and file name; at the end toss all files in one folder, sort on file name and then autonumber them all at once, then fix the Album tag and adjust the filename. Might sound cumbersome, but it all goes very smoothly in T&R...

/Michael