Another book is "Mac OS X Internals: A Systems Approach", although that was published in 2006 and does not include any networking (and the web site disappeared a couple years ago).

"Given the book's length, I chose to exclude several topics that are well covered in other texts. The TCP/IP stack is an example -- there is no "networking" chapter in the book since the Mac OS X TCP/IP stack is largely a derivative of the FreeBSD stack, which is already well documented. In general, information that is generic across Unix variants and can be found in standard texts is not included in this book."

The author, Amit Singh, was the original author os the MacFuse project.