I'm not an expert on TableMatrix, and if you want some advice, if you are experiencing trouble with it, I would dump the widget in favor of one that works for you.
I would implement something on a Tk::Canvas or Tk::Zinc. The canvas handles thousands of items and changes very well. It's a bit more work, but you get to control every aspect of your widget. I wrote Tk-CanvasDirTree as an educational example to show how easy it is to make your own custm widget.
The basic list and table widgets in Tk are simple widgets, and you can't expect too much from them.