Greetings;
Its been a while (as in 3 years) since I converted images with photoshop, so I will give you what I know from memory. I always got satisfactory results doing it with layers and the RGB filters, and adjusting the levels. Never, ever --[got good results from converting to gray scale. Your red, green, levels, work the same as applying a red, green, or yellow filter over your lense! They increase contrast. So, if you leave the colors in, you have a greater playing field of contrasts.
j