I did excactly this, about 10 years ago. I cut out the fitlite pads and used a traditional Jofa-liner instead. As I remeber it, the foam in the 6K was flush to the plastic and also had a large vented hole in the middle which made the modified pad less protective than the standard pad (Jofa 9090, originally 3190 I believe). Shots and slashes...didn´t feel so nice.
For recreational hockey it worked just fine, but I honestly remember the level of protection was a little to bad for my liking. Bought Reebok 11K after a while.