Try this viperoni:
The air is usually so stagnet around the 5 1/4 drive area, what you could do is buy a quiet 60mm (adda at pham) fan or 50mm. Move your silent drive as far back to the middle of the system on that drive bay but still keep all 4 screws, mount the silentdrive, at the very lowest 5 1/4 drive since there the most structure stiffness, less tendancy for vibration. Be creative and figure out how to mount this fan behind the drive right in the air path of the heatplates. Moving your drive as far back as possible is gonna probably leave more then 1 inch space from your front brazel/drive cover and you can line that up with acoustic foam.
HAve this fan sucking air blowing to the back of the system, the extra air presure might even cool your CPU down some, depending on your case it should be blowing right at it.