Perhaps it will help the OP to clarify the term rendering. 3dsmax produces lovely images, we think of this as the standard for rendering. It renders because there is a module in 3dsmax called a "rendering machine". Actually, 3dsmax has 3 rendering machines provided in the default installation. The user has to choose which upon making a render. One of the many differences between 3dsmax and Gmax was that rendering engines were removed from Gmax. Practically, that meant that to see your creation in a rendered form you had to export it to FSX, and then take a screenshot of your object in FSX. Now you can easily see that FSX IS a rendering machine of its own.
The key is that the render machine in FSX is primitive compared to any modern rendering machine. Therefore, you have to learn how to create effects for rendering in FSX by more primitive means in most cases. One example is normal mapping. For reasons I've never quite understood, FSX expects the channels of a normal map to be arranged differently from what you get if you use a nvidia normal map plugin, or the adobe version. This is well documented in the wiki of this site, so go read it.
When you make a render in any rendering engine you select, and position the camera, and the lighting, as well as tons of other things. In the primative FSX renderer, the camera and lights are set for you. Without light reflection, you would never see the effects of any normal map. The reason that you might prefer the appearance of a normally mapped model in a render from the 3dsmax engines, like mental ray or iray, if because those engines handle light in a far more realistic mode (assuming you activate those settings). Light management in FSX is one of the many areas in which FSX takes "shortcuts" compared to Iray or Mental RAy. By the way, these short cuts are needed, because the makers of FSX intended it to be a simulator capable of rending new images in 1/30th of a second. The fabulous renders you see in 3dsmax can take anywhere from a few minutes to many many hours using distributive computing to generate. Totally impossible for a simulator.
So what we do when designing for FSX is attempt to provide FSX with the right "overhead" to get the best rendering to occur, and we accept the constraints of the FSX renderer.
A common way to acheive this is to provide both 3dsmax and FSX with an image that serves as the material in 3dsmax, and is converted into what FSX calls a texture. The idea of baking ambient occlusion that folks have discussed above is a process of taking an effect that you can easily ask IRAY to render, and "baking" or adding it to the image that we'll use as a texture in FSX just because FSX CAN'T natively render ambient occlusion.
I hope these comments make the many answers you've read in this thread perhaps a little clearer. Most of us find that photoshop is helpful for creating that image that we'll use two different ways.
One note I'll add in conclusion is that 3dsmax actually includes photo-editing capability internal to the program. You can create distorts, paint, make layers, and you have most of the filters for displaying the results of layers (like multiply, burn, etc.) as in photoshop. Its not something I've used in 3dsmax, because I have photoshop and I'm very used to it, but I found that part of 3dsmax recently, and was a bit surprised by seeing it.