My two cents worth might help...
I did have all of these problems; very frustrating. I called tech support, left a message and had a response in about two hours.
Here's something that really confused me about Halion Symphonic Orchestra until I spoke with tech support...it is 'not' a stand alone instrument; it is additional sounds that are to be accessed through Halion Sonic 2(SE). So...
Add an instance of HSSE to your instrument rack.
When searching, be sure to turn on the 'filters' tab so that the 'categories' are visible.
At the top of the first category list (in blue) on the left, there is a dropdown menu; go to submenu 'Audio - Assets'; continue to a second submenu and then set it to "Library Name". Now you will see your Halion Symphonic Orchestra library.
From there, select like any other instrument.
I have another problem, if anyone reads this thread that has gotten beyond this problem.
I have a midi 'strings' track for HSO, but when I export to audio, the audio level is like -40db. I have the audio fader and the midi fader at 0 and the velocities are quite high on the file. What am I missing here?