Unclear relation of hex codes to the HID Table

Hello, I want to map Rewind (0xB4) from http://www.freebsddiary.org/APC/usb_hid_usages.php
to one of my pedals, but `-S 'B4'` doesn't seem to work.

I also don't understand where the values for XF86AudioPause (0xe8) in `common.c` come from.

Any help would be appreciated :)