I was actually going to come in to say this. Not only was it a great version of the song, but for a giant like Cash to cover a smaller - but still significant - band like NIN so late in his career is an unbelievable tip of the hat.
Runners up for me are Don Henley covering Leonard Cohen's "Everybody Knows":
Henley really takes an incredibly heavy song and keeps it heavy, but also makes it a lot more jazzy and energetic.
And Dream Theater covering Rush's Xanadu:
It's a challenging song with a really unique sound and it took a band with Dream Theater's technical abilities to not make the song dumber in their cover.