For any type of vocal music, you want dt880. I prefer 880 over 990 for almost everything. Their tone is much more natural, sounds more realistic. The bass is NOT shy by any means, sure, the 990 has got more of it, but not as deep to my ears. This is probably because of a bump right before the deepest bass, which masks the very deepest bass. The dt880 do not have this bump, and therefor sounds deeper in comparison.
DT990 might be more "fun" on some records, but those records are far a part. Every vocal has got some odd harshness, like an extra bite. This might make it more fun, but also sounds unnatural. The harshness is only in comparison to other cans. While DT990 was my only can, I did not find them harsh in the vocals.
There is one record which dt990 do better than any can I've tried. And that is Mastodon - Leviathan. It's pretty much the reason why I'm keeping them at the moment.
If you are sensitive about prominent hights, 990 are not for you. They have very prominent hights. If the recording is not very good in the hights, it might mask everything else with a SssSssssSssssSsssSsss. 880 can have this also, but the hights are not as prominent and don't mask everything else if that happens.