The default M6Start macro is this:
tool = GetSelectedTool()
SetCurrentTool( tool )
If you want to move to machine zero, change it to this:
tool = GetSelectedTool()
SetCurrentTool( tool )
Code "G53 G0 Z0"
While IsMoving
Wend
Code "G53 G0 X0 Y0"
While IsMoving
Wend
Make sure that Z zero in machine coordinates is the top of your travel, or at least some distance up that is safe to move at.