Is there a way to set a D3DXMatrix to a float[16] if you want to use a custom built matrix or must you set each element one by one?

You can create a D3DXMATRIX using a pointer to 16 floats as a constructor parameter - according to the struct definition you can do any of these:

D3DXMATRIX() {};
D3DXMATRIX( CONST FLOAT * );
D3DXMATRIX( CONST D3DMATRIX& );
D3DXMATRIX( CONST D3DXFLOAT16 * );
D3DXMATRIX( FLOAT _11, FLOAT _12, FLOAT _13, FLOAT _14,
FLOAT _21, FLOAT _22, FLOAT _23, FLOAT _24,
FLOAT _31, FLOAT _32, FLOAT _33, FLOAT _34,
FLOAT _41, FLOAT _42, FLOAT _43, FLOAT _44 );