Try this code:
- stiffness matrix:
*DMAT,MatKD,D,IMPORT,FULL,file.full,STIFF
*PRINT,MatKD,Kdense.matrix
- mass matrix:
*DMAT,MatMD,D,IMPORT,FULL,file.full,MASS
*PRINT,MatMD,Mdense.matrix
- damping matrix:
*DMAT,MatCD,D,IMPORT,FULL,file.full,DAMP
*PRINT,MatCD,Cdense.matrix
If you can't do it in explicit dynamics try different type of analysis. Matrices should be the same regardless of the time integration method.