Aren't the S6 biscuits the giant whoppers?
If so you have to do a double plunge, it's not enough to set the plunge depth to max. You have to plunge once then move the machine a few mill to the left or right (there are marks on the base plate to show you the required off-set) then plunge for a second time.
The process is written down in the manual, but it's not particularly obvious, anyhow keep hunting in the manual and you'll find it and when you do it's all pretty straightforward. The only issue is that the off-set double plunge routine makes laying out the reference marks on the workpiece a bit more complicated, but you soon get the hang of it.
Good luck!