ampan, all you need do is look at the flight plan that was included with the briefing. It calls the point down in the bottom of the sound, 27 miles away from the real McMurdo, McMurdo. So the audio mentioning only reinforces the flight plan positioning of "McMurdo", particularly in light of the fact that the maps indicate tracking to the false "McMurdo" position as well.
One wonders why there was no leg on the flight plan from the false McMurdo to the real McMurdo in the event they needed to make an IMC descent in the earlier flights. Could it be because the nav dept had absolutely no idea where the false McMurdo was placed?
6,000ft minimum descent was a strict CAA rule when approving these flights. I very much doubt anyone could say an invitation to descend to 1,500ft by an Air Traffic Controller could in anyway overrule this CAA requirement.
So you need to answer why Captain Wilson in his briefings told crews they could go below 6,000. I have no idea of the reason, and I doubt you do either.