HSO - can't load more than a single instrument?

I’ve been using Steinberg String Edition 2 for many years and the interface allows you to load 16 instruments vis 1 instance of the VST plugin.
I’ve just updated my system to 64 bit (with Cubase 8.5 Artist) and installed the HSO demo.
When I look up HSO on the web (for example the Sound n Sound review) the interface looks similar to String Edition, with 16 midi channels to load patches and an online PDF manual shows this too. However, my version has a different inface and I can’t see how to load more than 1 channel.
Any help please?

Not sure what interface you’ve looking at. I did check the review article, and it doesn’t look like that anymore. HSO is loaded as a HALion sound. HALion itself provides multiple slots for multiple patches, which could all be HSO. It looks like this on my system:

Same issue, is this a bad GUI or bad software?

Click the downward pointing arrow on the right side of the midi slot to fill.
A box will pop up. Select HSO and then select the sound you want to use.
Each channel is done the same way.

Just been reinstalling all my software on system rebuild on a Mac for Catalina. Comparing my Mojave vst3 plugin directories I noticed there was a HSO.vst3 plugin.

I assume this was for the HSO sound player, presumably used as the sounds player before Halion Sonic HSO sound file integration was introduced. (Perhaps it used the HSB sound file formats)

I tried the plugin and got the lock up effect the OP referred to (will not allow the default loaded sound file to be changed), so Im guessing this plugin is now redundant with Halion Sonic integration and can be discarded from use on systems able to run Halion Sonic.

Been unable to get the HSO vst3 plugin to work on OSX 10.14.6 (Mojave) and 10.15.6 (Catalina). However plugin manager in Cubase gives no plugin errors.

Presumably the plugin has never been updated due to Halion Sonic developments, but is not deleted on Halion / Halion Sonic installs which now run the HSO vstsound libraries. (assuming you have a HSO licence on the dongle).