I'm not sure I understand the question. If they're doing zoom-in CIH, they don't need a scaler. They just project the image so that the empty letterbox bars overshoot the top and bottom of the screen.
You say "of 16:9 movies." Does that mean 16:9 discs (of which all Blu-rays are), or movies with a 16:9 (or 1.85:1) aspect ratio? Arey they trying to crop a 1.85:1 movie to lose picture off the top and bottom and fit onto a 2.35:1 screen? If so, why? That will look awful for most movies. Or are they looking to shrink a 1.85:1 movie to fit in the center of the screen with pillarbox bars on the sides, which is a different thing entirely?