When I first downloaded, there were 4 files and after the download, the one I mentioned, Endeavour S06E01 HDTV x264-MTB [eztv] would not play even as an AVI.
I had to download it again. And maybe because as you say, my CPU was pretty well maxed out, that was the reason?? However, alls well that ends well.
OS 10.12.6 iMac (Retina 5K, 27", 3.4 GHz Intel Core i5, 24 GB RAM, 2400 MHz DDR4. Sierra. 10.12.6 SuperDuper. 1 TB Lacie HD, Noise Ninja.