Edward, the problem with using IDC and the camera's creative styles is that you're not getting an accurate histogram representation of the RAW data, and you're more than likely underexposing more than you realize. If you have zero issues with the camera's noise handling, then this is a non-issue, I guess. However, if you have qualms with the A900's noise, it's essential to set the camera's jpegs settings to achieve the closest histogram to RAW that the camera can muster, and leave it there. This will reduce the noise quite a bit. When using IDC in your workflow, you're taking a shot underexposed, then the camera jpeg engine boosts the histogram with all of it's "special sauces" like contrast, saturation, etc. When you open the RAWs in IDC, it also applies the same "special sauces," leading you to believe that you were exposed properly all along, when, in actuality, your shot was underexposed, and both the camera jpeg engine and IDC boosted the shot, causing the histogram to look correct. This gaining up of the underexposed shot adds lots of noise.
Does all of this babbling make any sense?