You have installed those extensions before. The installation was successful and they were shown in EM at that time. But now only one of them is shown. Is it correct?
If it's correct, one possible reason is that you deleted the corresponding .zxp (or .mxp), .mxi, .mxi_air, .mxi_path files in EM_Store folder ("C:\ProgramData\Adobe\Extension Manager CS6\EM Store\Dreamweaver CS6" or "C:\Users\<YourUserName>\AppData\Roaming\Adobe\Extension Manager CS6\EM Store\Dreamweaver CS6") accidentally.
Another reason is that you might have input some search string in the search box so the extension list was filtered out. Please make sure the search box is empty.
You can install those extensions again. the new installation will overwrite the old one and then they will be shown in EM.
Installed on a different computer with Windows XP operating system and is just fine. All the extensions show for Dreamweaver in the extension manager.
When Dreamweaver extensions are installed on my new computer with Windows 8.1 operating system only one Dreamweaver extension shows out of six in the extension manager! But when I go to Dreamweaver they are all the and seem to be operating ok thus far. I am only asking my original question because I would like to know how to remove the extensions from Dreamweaver should there ever be a problem and a need to do so. In my understanding is that the extension manager is the only correct way to remove the extensions from the products that they are applied to.
*** Note: the installations are all first time installs on the Windows 8.1 operating system computer. No deletions, or re-installs have been accomplished --- first time for all Design & Web Premium CS6 and all Extend Studio Extensions for Dreamweaver.
During you installed the five extensions which is not shown, have you seen any error messages popped up?
No error messages --- none at all looked as if everything was going well!