Cubase Artist 6 and Cubase Essential 5

I have Cubase Essential 5 Full Version.
And I am about to buy Cubase Artist 6 Full Version not upgrade.
I have heard that Cubase Artist 6 is higher version than Essential 5.
But Some features (for example - number of midi tracks and instrument track)
are smaller than Cubase Essential 5. Why???
And Can I use Cubase Essential 5 with Cubase Artist 6 Dongle key???
Lower Version’s license is compatible with Higher version’s one, isn’t it??
Please Answer~~