Okay, same thing for hex. It appears that the code wants it spelled out completely, as in "0x00000006" rather than "0x6" or simply "6". Pity it's so pedantic about it, but that's how it works.

Here's the "Bottom" button again, using hex:

echo 'BUTTONRAW=0x00000006' > /proc/empeg_notify
# wait a second or so, then release it:
echo 'BUTTONRAW=0x00000006.R' > /proc/empeg_notify

And next, using the button you were trying (0x20df03), which is actually the SOURCE button, not MENU:

echo 'BUTTONRAW=0x0020df03' > /proc/empeg_notify
echo 'BUTTONRAW=0x0020df03.R' > /proc/empeg_notify

Note that using BUTTONRAW requires real-time approximation, as buttons do change function depending upon the interval between press and release.

Hope this helps!

-ml