Sounds like I better put writing the next LIDAR tutorial higher on my priority list, you are all getting close to figuring out how to get a LIDAR terrain into APCD!
A lot of the magic happens in QGIS. I create a point grid to sample the raster LIDAR data to the desired density, same as in the green contours tutorial. I go to the attributes table for the points and multiple each by 10 and round to an integer number. Then create a raster from the point grid with the 10x elevations as data points. I also add a buffer ring of 0 value elevations around the grid. This helps with the small .dem import screen in APCD and facilitates the terrain scaling.
When doing a constrained z scale in APCD, the average height for the terrain does not change, but the extremities of the heights do (the 0 value buffer verts). The distance between the average terrain height and the 0 value verts gets scaled to 1/10th. So what I do is take a small section of the 0 value verts and raise them to where they will be after scaling. That height will be AVG - 1/10*AVG. For example, if the average terrain height is 400, raise the small section of 0 verts to 360. Then for the constrained z scaling, select all the terrain verts but NOT the raised verts. When doing the scaling with the mouse, do not let go until the surrounding 0 verts line up with the height of the raised verts. The scaling must be done in one motion to get a true 1/10th scaling. When the constrained z scaling is complete, select the entire terrain again and move it down so that the 0 verts are back to being 0 height. The verts moving motion is forgiving, it usually takes a few attempts to get them back to 0.00 height. When finished I delete the buffer ring of 0 verts so that the dimensions of the terrain exactly match what is in QGIS which helps the placement of the overlay texture.