Hi Woof-
Not sure if you have gotten any help after all this time; but I just happened to come across this post today- if you've already been helped, maybe someone else will find it useful.
This is the method I have been using until I was done converting my collection- then switched to audible.com
To join .m4b extensions- first change the extension to .m4a
Next use a program called
YAMB. With this program, you can now merge your audiobooks; so instead of having multiple parts- this will merge that particular audiobook into one file.
Next- after the merge is completed, rename the extension .m4a back to .m4b (so that they'll appear in the AUDIOBOOK section of your iPhone/Pod/Touch.
Next, you may want to use a program like
Markable which will add bookmarks to your story- without the bookmarks, you have one long story that doesnt know its place when you stop and want to come back to it.
All of this was done on Windows; I have no idea what programs will do this on a Mac.