[quote user="danishinnis"]Updates aren't supported for beta 4, but I'll look into this[/quote]In case it helps, on a different CCSv6 beta 4 installation on Windows XP (rather than on Linux) was able to install the emupack 5.1.450.0 update without error.
Not sure if the Linux update was corrupt, or I suffered an one-off Eclipse "glitch".