Still not sure what look you're going for, but if you want to make your blacks blacker and your whites whiter, use the Levels feature by bringing the outer triangles closer to the middle triangle. Or use the Curves feature by making an S-curve to increase the contrast between highlight and shadow. To get a really good grayscale, I'd suggest using the Lightness channel in the LAB color mode. FWIW, I hope that helps.