I have a 12x16 inch Nova fibre.
It has four slanting slots. For RC paper you just use the clip as per the other processors but for fibre paper you use the paper holder. You slide the paper into position onto the holder which supports it at the bottom and holds it back at the top. With the slanted slots the paper will sit back on the holder. Then you can move the holder from slot to slot. It's a great system once you get the hang of slipping the paper into the holder. For 10x8 inch fibre I just use the clip and switch to the holder for my 12x16 paper.

You can do fibre in a big quad but it can be tricky. The fibre holder probably won't be of any use as it needs a slanting slot to work but you could try it, I suspect the paper will just buckle though. I've heard that many folks use two clips to hold 12x16 inch fibre paper and gently move from slot to slot in a quad.