Thanks! The synth is Dreamtonics' Synthesizer V, using the SOLARIA voice database from Eclipsed Sounds.

What really sold it to me was listening to some beautifully crafted covers from this YouTube channel: https://www.youtube.com/watch?v=KX0lcVr9ugI

Prior to this, I'd been experimenting with pitch-shifting the output of Google's Text-to-Speech service (https://cloud.google.com/text-to-speech), which was quite interesting and somewhat pleasant sounding for spoken word vocals, but didn't really have the range or expressiveness I was looking for more generally.