TT2M works with a GMS grid. It converts the TOUGH2 node data to a “3D scatter point” file that can be imported into GMS. Then for visualization you need to interpolate this 3D scatter point set to the GMS grid. I work exensively with geologic modelling to create geologically realistic tough2 grids and find that GMS is very usefull. Visualization is also good. To do what you want you need to create a grid with GMS that is comparable to the one you have.
In the long run, you should consider creating the grid with GMS... The new Beta version of GMS has already Voronoi gridding and I am in the process of updating TMT2...