I managed to compile the 18.104.22.168 kernel with sound support with the intent of getting the Soundblaster x-fi usb working, without success so far. I was wondering why you want PCI if you are going to install the modified kernel on a MBWE?
Since I cannot post the link, check out the Hacks and tutorials page of this website for "How to Revive Western Digital My Book World Edition ". It's for the blue light edition, but with some changes for the names of some configure files, it is pretty much the same.
That is where I got much of the information. He sets up the crosstools, tells where to get the WD latest source and configure and compile it.
His intent was to create a loadable module to use with a Debian root system. Of course, with the current boot images, the kernel must be written to /dev/sdX where the X indicates the device letter as seen on the host system that the drive is connected to.
I first cleared the kernel area by writing Zeros to that area which = count of image size / 512
dd if=/dev/zero of=/dev/sdX bs=512 seek=336 count=2929
The compiled kernel can be written to the drive with the commands:
dd "if=/path/to/kerne/limage of=/dev/sdX bs=512 seek=336
That is an offset of 172032 bytes from beginning of drive.
Of course the caveat is "attempt at your own risk."
I don't remember exactly where I found the scripts to unbrick the MBWE but it was through the MyBookWorld wikidot website. It downloads the latest image, unpacks it and writes it to the WD SATA: it saved my butt many times while experimenting on my own MBWE.
By the way, I'm still trying to get that USB Soundblaster X-Fi working.