
I think here you have to select your STEAM folder so Omnisphere knows where it is, as well as where you want the VST. Inside the "Software Update 2.5.0d" folder, right click the "Omnisphere Software Update.exe" and run as Administrator.It should look like this, these are the properties of the shortcut file I've got. Create a folder called 'Spectrasonics', then create a shortcut to the STEAM folder inside that folder. Go to C:\ProgramData (it's hidden by default, you can turn hidden items on like this in Windows 10 or like this in other versions.

Place it wherever you want (root of C:\ drive is preferrable, this is what mine looks like. Unzip or mount 20180906_120200.iso using WinRAR or Windows 10's built in ISO mounter, this.

Place it in a place convenient for you (~ 83GB). This folder contains Omnisphere 2.3.2h POWER SYNTH from the release of Omnisphere, Keyscape, Trilian. As a result, you should get a Spectrasonics folder with such contents (See pic).
