Thanks for your question, DRMman. I wasn't able to get sound and video to both record well on the same program, so I use XBox Game Bar which comes with my Windows 10, just to record the video footage, with the sound muted.
To capture sound I run the demo (.lmp file) while recording the speakers output in Audacity. I also use Audacity with a Snowball Ice microphone to record and edit my commentary. Finally I use the editing program Filmora 9 to bring together the Audio, Video and Commentary before adding extra effects and finishing touches.
I made another video public on 3rd June after going back to Underhalls for some more speedrunning. Enjoy!