Xmax is mostly a function of voice coil length and length of the pole piece.
Vas is partially described by you but in greater depth also is realted to the material selctions of the cone,surround and spider which affect the phyiscal properties of a driver.
When a driver is connected to an amplifier the electrical items come into play.
Fs that is desired by the designer can directly affect the Vas since it is an acoustical equivalent what free air is behind the driver.
