I and one or two others had problems with the HSSE Hybrid set install. Mine was from the full boxed DVD version.
There was a specific thread on the subject where I posted a workaround. When I searched, the thread had been combined with the general missing content thread even though I’m not entirely convinced the two issues are related.
Anyway, the original thread was titled ‘No Halion Sonic SE Hybrid Sounds ?’ you can follow it at the bottom of page 6:
My workaround appears midway down page 10:
Although the subject is placed within a thread listed as [SOLVED] I’m not sure whether this issue remains on some systems.
Hope this at least gets your Hybrid sounds installed.