You are right with the fist one.
When it comes to Acer x freemanii 'Armstrong'. It is
Geslacht= Acer
Species= x freemani
Culture varriety= 'Armstrong'
The x stands for a cross breed
As I understand it the 'x' denotes that the plant in question is a hybrid between two species as in;
Phygelius x rectus this is a cross between Phygelius aequalis and Phygelius capensis.
OR
Salvia x sylvestris a cross between Salvia nemerosa and Salvia pratensis.
OR to complicate it a bit more;
Salvia x superba a cross between Salvia nemerosa and Salvia x sylvestris.
So the x is with the species name because it stands for a hybrid.
NOTE THERE IS A DIFFERENCE BETWEEN CULTURE VARIETY AND BOTANIC VARIETY. BOTANIC VARIETY ALWAYS ISN'T SET IN ''" AND IT CAN BE PERCIEVED BY var. BUT IT CAN BE PUT AWAY.