It’s difficult to compare the HSO plugin directly the HSO VST Sound Instrument Set in HSSE because the presets seem to be very much simplified in the HSSE soundset but in the HSO plugin, the presets are set at 0dB output level whereas in HSSE they are at -12dB by default.
Therefore the difficulties people are having are not only because they are not aware of the need to use the mod wheel (although that, and needing to RTFM is by far the most common problem) – the presets are in fact different.
If you load “Vln solo combi Vel KS_16” in the plugin, it’s louder than “Violin solo combi” in HSSE with mod at 127.
This is purely academic though because the differences are easily compensated for within HSSE.