Hi,
HALion Sonic SE is discontinued as it’s place is now taken by HALion Sonic 7. We wanted to make it clear that one version is for playing and HALion 7 is for playing, design and development of VST Sound files.
Regarding the installation:
HALion 7 replaces any older versions of HALion. Existing rojects usually load just fine, we have put a lot of emphasis on backward compatibility.
HALion Sonic 7 replaces all older versions of HALion Sonic. If you load a project containing HALion Sonic 3 or HALion Sonic SE 3, it will replace those instruments. This should also “just work” as we also invested a lot of work to make this seamless as possible. EDIT: This does only count for Cubase and Nuendo! Third party DAW might still try to load old halion Sonic SE!
We decided to leave the discontinued HALion Sonic SE 3 files in place, since some, few, people still use old legacy VST instruments wich are now part of the VST Sound library.
I hope this answers the question.
In any case, check out HALion Sonic 7. It is free after all 