Here's how to get TypeMatrix (or any other keyboard for that matter) multimedia keys work on FreeBSD:

http://wiki.freebsd.org/uhidd

Notes:
* When you run uhidd don't use -k flag. This will screw things up with TypeMatrix (Edit: actually this depends on kernel config)
* For Xorg key names, check files in /usr/local/share/X11/xkb/symbols
* Until you have configured uhidd I recommend having PS2 keyboard around. Because
when you will launch uhidd for the first time to generate cc_keymap file, typematrix might not be very usable.
* Don't quit uhidd (when you launch it for the first time) until you have copied cc_keymap file... otherwise it will be removed
* xev might not show that you have pressed key, if it is intercepted by your Window Manager.
* The Eject, Power, Sleep, Wake buttons still won't work (AFAIK)

My personal config (Might not work for you. Who knows....)

/usr/local/etc/uhidd.conf

0x1e54:0x2030={
cc_keymap={
Scan_Next_Track="0x63"
Scan_Previous_Track="0x62"
Eject="0x60"
Play/Pause="0x6F"
Mute="0x5F"
Volume_Increment="0x5A"
Volume_Decrement="0x54"
AL_Email_Reader="0x72"
AL_Calculator="0x71"
AC_Home="0x74"
AC_Back="0x7A"
AC_Forward="0x75"
}
}


~/.Xmodmap

keycode 92 = XF86AudioLowerVolume
keycode 170 = XF86AudioRaiseVolume

keycode 207 = XF86AudioPause
keycode 184 = XF86AudioMute
keycode 190 = XF86AudioNext
keycode 189 = XF86AudioPrev
keycode 219 = XF86WWW
keycode 210 = XF86Mail
keycode 209 = XF86Calculator

keycode 220 = XF86Forward
keycode 130 = XF86Back


/etc/rc.conf

uhidd_flags="-o"
uhidd_enable="YES"


Launching xmodmap is desktop specific, so I won't mention how and when I do this