Worm-Infested Intestinal Tract said:
Avoid anything remotely not underground.
I guess that eliminates anything i could suggest, since you were being so exact with the genre's
As for goregrind, Lord Gore, Myopia, The county medical examiners are probably the lesser known ones that i really like...also check out razorback records roster, they have a lot of goregrind. I advise you to stay away from Regurgitate also when it comes to goregrind.
NSBM the ones i like are Graveland and Burzum but they probably aren't your consideration for underground because anyone into underground metal will know about them
If you just want black metal i can help with underground bands probably.
I don't listen to much of the other genre's except Death metal...maybe you'll like Visceral Bleeding, spawn of possession, Exmortem
Catchy riffin' power metal that is underground loses me...only power metal i really listen to is Nightwish(if they're considered power metal, i'm bad with genre's) and Hammerfall...a bit of Dream Evil...and haven't checked out Elvenking but should.
Hopefully i helped some but i doubt it