I haven’t tried it, so I can’t really offer opinions on it specifically, but I have tried other speaker modelling software. Years ago someone at Dolby made some and they sounded amazing. I put them on and when I heard sound, I took them off because I thought there was something coming from the speakers.
When slate came out with these headphones, I went to to try the waves version to see if I was missing out on the idea. I found the waves version to be a gimmick at best, annoying at worst. After 10 minutes with the demo, I knew that I would never need it or want it.
So basically, my experience is that when done right, it can sound really good. When not done right, it’s totally lame. I have no idea where the VSX falls on this scale.