I would assume you are refering to the Signature G5 and G6, if so, the G6 is the current Siltech's top range signature series that replaces the old Signature G5. I do not know about the Emperor in partcular, but I heard that in general the new G6 is more neutual, quieter, and pretty much better or as good in every aspect comparing to the old Signature G5. However, the Signature G5 is warmer sounding, so some would prefer it over the G6 because of it.
There is also a current G5 Classic series, which is one level below the G6 signature series, and they are a lot less expensive, and less capable.
There is also a current G5 Classic series, which is one level below the G6 signature series, and they are a lot less expensive, and less capable.