To enable homebrew like multiMAN, you must first install Hybrid Firmware (HFW). Prepare USB : Format a USB drive to and create a folder path: PS3 > UPDATE Download HFW file, rename it to PS3UPDAT.PUP , and place it in that folder. Update System : Plug the USB into the rightmost port of your PS3. Go to Settings > System Update > Update via Storage Media and follow the prompts. Install HEN : Open the PS3 browser, go to the site, and use the HEN Installer/Enabler
HEN stands for Homebrew Enabler, a software tool that allows users to run homebrew applications on their PS3 consoles. Homebrew refers to software that is not officially supported or authorized by the console manufacturer (in this case, Sony). HEN exploits a vulnerability in the PS3's firmware to enable homebrew execution.
Since you are on HEN (likely a converted CEX console or using HFW), the installation process is slightly different than a standard CFW console. You do not need a "DEX" version of multiMAN; the standard "CEX" version works perfectly on HEN.