QTR-Quadtone RIP

To clarify: there are two different things here that should not be confused: the color MODEL of the image (maybe RGB, Lab, CMYK, HSV or whatever) and the color SPACE (with related color PROFILE). I'm referring here to the space/profile not to the color model. I'm not on a computer with Photoshop at the moment, but from the top of my head you can convert your file via the edit>mode option. QTR comes with an QTR-LAB.icc profile. If you install that in your profile direction, you will see that as option while converting your file.   

Joost