Thanks heaps J for those suggestions. I've downloaded the Foobar plugins and will give those a try.
For most other situations where I want to upmix stereo to HOA, I've come up with an FX chain using a variety of plugins that does quite a good job pulling the image completely around the listener.
There's a NuGen 3D upmix plugin that I'm interested in demo'ing but I don't want to try it until I have the funds available in case I really like it!!!
I haven't been that impressed by their past offerings but some reviewers claim this is in a totally different class quality wise. Perhaps it is... Perhaps not.
https://www.nugenaudio.com/halo-upmi...-aax-au-vst_52
I have to say though that overall, my need for such elaborate upmixing is becoming less and less. I'm pretty much working with my own original compositions these days so my projects are mostly mono, stereo and multi channel sources placed in the 3D field with the Ambisonic tools I already have.