Seems like developers are still seeing the importance of making addons compatible with FS9 even though the platform is 11 Years old!
REX Soft Clouds FS9 Edition is the new volumetric-like soft cloud texture add-on for FS9 (FS2004). This soft cloud pack gives a true volumetric feel to your flight simulator clouds!
This package is compiled from years of feedback from current REX customers to meet a specific demand! REX Soft Clouds FS9 realistically enhances the FS9/FS2004 cloud environment. You will also truly experience better haze and fog generation.
They also say they’ve made it optimised for both High and Low end Machines and additionally very frame rate friendly!
For more information click here