I use to cut 8 ply mat boards with two logan cutting heads along with the logan straight edge. On the bottom of the cutting head you will find a blade depth screw. The first head should be set for 4 ply and the second at 8ply.
After the the measurements have been marked. I score lightly with the 4 ply head once and then again all the way down.
I then use the 8ply head and score lightly and then all the way down.
I was usually cutting rag mats and I would switch both blades after each cut which would be a total of 8 blades.
Blades are cheap and 8 ply rag mats are very expensive, so I find that the cost of 8 blades to do a clean job is cheap.
Just plan on sacrificing at least two boards for the learning curve, but once you have it down, it's pretty simple.
Art work that has been matted with 8ply board looks very elegant and I highly recommend it.