@Jsabinpa In short, the Maslow cannot plane a surface smooth, however, you can use a maslow to help build a router jig that will allow you to do just that. Here’s a link to the cut files: Slab Flattening Router Jig
EDIT: You are on the right track as far as CNCs in general, btw. Some CNCs do allow you to smooth rough-cut lumber, but short of spending $8k+ for one of those (Gantry-based machines), using the manual process really isn’t a bad way to go. I did it for this table project: Legs for Kitchen Table
Here’s the specific post talking about flattening the slab:
I used this bit: http://a.co/2LUitlL
(And depending on your router,
you may also want this extender to make the job easier: http://a.co/az2abLt)
Hope this helps!