I’ve purchased HSO yesterday (and also Halion Sonic – until yesterday I didn’t realize Halion Sonic and Halion Sonic SE are different things). HSO is basically a set of sounds for HS/HSE, it appears inside HS interface as an additional soundset. I’m sure it is fully compatible with your setup. It would be compatible even if you only had HSE, but in this case you could only use it inside Cubase. HS works under other hosts too. Works for me in Logic Pro.
As for HSO audio demos, I had to search for them on youtube… It’s ridiculous that this kind of info isn’t easy to find on Steinberg’s site. HSO is orchestra-oriented library, so it’s not just better samples than you already have in HS/HSE, they are more detailed - instruments have different articulations and sometimes different samples of same articulation.