In my room, I have had an STF-2 and a VTF-3MK1(with the non-BASH amp and then replaced with the BASH amp). I now have a VTF-3MK3.
The STF-2 is now with my brother, a second STF-2 is in my Parents' family room(with a Ventriloquist speaker set), and my old VTF-3 is in their livingroom.
Music is more important to me than HT, and if my experience with these three subs is any indication, you will not lose anything going from your original VTF-2 to a VTF-2MK3 and will gain more extension and output capabilities. Blending will not be a problem.