I found that Dirac Sensaround II doesn't destroy the HRTFs already present in stereo sources. With other renderers like Waves NX on the Audeze Mobius, you must disable any HRTFs at the source - set the game to non-HRTF "Stereo" or "7.1" instead of "Headphones", disable "Dolby Atmos for Headphones" or "DTS Headphone:X" etc. Even if source HRTFs are enabled, they are seemingly destroyed and sound only comes from the front virtual speakers, so you might as well run the source in non-HRTF "Stereo".
Dirac Sensaround II expands the soundstage but the original positional audio from the source HRTFs are preserved. I tried it with games in "Headphone" mode, and in 7.1 movies downmixed to stereo with "Dolby Atmos for Headphones" and "DTS Headphone:X". By default, "Dolby Atmos for Headphones" has a small but positionally accurate soundstage, and "DTS Headphone:X" has a wider but still positionally accurate soundstage. Dirac Sensaround II expands the soundstage further, but reduces positional accuracy a bit. This is a surprising result as I expected stacking HRTFs to destroy each other. This is similar to the Dolby Surround Upmixer on Atmos AVRs which accurately places stereo source HRTFs in a 5.1.4 speaker setup.
It's great for ear-piercing mono sounding YouTube videos, and it's not too bad if you accidentally leave it enabled during HRTF content.