I would suggest that you reduce the gain on that tone, such low tunings require less gain to sound decently clear. I couldn't really make out the riff most of the time. Maybe add some more EQ to clean it up, maybe that'll allow you to bring the guitars up a bit, cause currently the drums seem to be the loudest part of the mix.
Also, I get that it's hard to play, but I think the track could really benefit from double-tracking.