I second this. If it can be solved it would be massive. Lots of bassy voices that currently don't convert well enough, or parts of songs. Like Opeth isn't there yet, or The Tea Party, Cannibal Corpse forget about it lol.
On a more kind of mixed side you've got Pearl Jam. Lots of songs convert fantastic, but he tends to have this real low bass tone in some songs that never gets picked up.