One thing I should mention, since we get asked about HITS a lot at Dynon:
HITS doesn't come from the HSI.
To draw HITS, you need to know the full 3D path of the course you want. For instance, you need to know the actual glide slope angle, where the runway is in the real world, and where you are in the real world. An HSI doesn't know any of that. It just knows if you are left, right, up, or down at that given moment. A VLOC radio also doesn't know any of that, it just knows if you are above or below the beam right now.
To draw hits you need a database of approaches. The system needs to know you are tuned to the ILS at Aspen, and the glide slope there is 3.50 degrees, not just the 3.0 "default" which can ruin your day at a lot of airports.
All of this is of course possible in a well integrated system that knows a lot, but it isn't just as simple as drawing the HSI as boxes on the PFD screen.