I found these four files on my old Windows 7 machine which I have executed under Windows 10:
HALion_Symphonic_Orchestra_Installer_win.part1.exe 1480008048 03-APR-2018 11:15:06 [A]
HALion_Symphonic_Orchestra_Installer_win.part2.rar 1480000000 03-APR-2018 11:57:51 [A]
HALion_Symphonic_Orchestra_Installer_win.part3.rar 1480000000 03-APR-2018 12:34:26 [A]
HALion_Symphonic_Orchestra_Installer_win.part4.rar 1472997786 03-APR-2018 14:03:13 [A]
The exe installs the “Steinberg Instrument Set HALion Symphonic Orchestra”.
And the following extra now shows up in Control Panel as being installed:
Steinberg HALion Symphonic Orchestra VST Sound Instrument Set Version 1.2.0
In the Plug-in Manager, I now have two HSO’s:
HALSymphOrch VST 2.4, File: HalSymphOrch.dll, version 22.214.171.1242
Symphonic Orchestra VST 3.6.13, File: Symphonic Orchestra.vst3, version 3.3.1
Everything now works!
It was lucky I kept these as the Steinberg download area does not appear to have the Instrument Set installer.
The link https://www.steinberg.net/index.php?id=sound_content_downloads&L=1 just goes to the Download Assistant download itself - not to any other download.
In the Download Assistant, under VST Instruments and Plugins, and selecting HALion Symphonic Orchestra, only the vstsound files are downloaded, not the installer to install them - as far as I can see.
I now need to try to uninstall the old version (difficult as it’s not in Control Panel) and delete all the extra copies of vstsound files I’ve accumulated.
Thanks for your help.