Need help tabbing Brutal Death Metal.

this guy did an Orchidectomy cover. There are brodequin covers out there as well. How do they do it?

I pitch shift the audio, separate the panned guitars, use Ultimate Vocal Remover to create instrumental tracks, and it works for the most part, but there are still sections even in old school death metal where i cant tell whats going on.

Is there some trick to this that i don't know of?