Imagine the engineer being surprised about the humans ability to create something so beautiful as music and being impressed about it. maybe even changes his minds about destroying them and then BAM, he takes a axe to the back and says ''screw this shit'', back to killing mode.
So far from what i see so far it seems that these are alternate scenes just like the ones with Firfield. Ridley filmed both variants just like he said when he was in production. One version for a pg-13 cut and smaller run-time,and another version for a r rating and longer runtime. The only question is why the hell don't they release the whole cut. Right now because these scenes are added as a bonus, i doubt we will see another directors cut in the coming years since all the scenes are available. Shame