Hi,
I have just bought a Huawei P9 (Android 6.0 / EMUI 4.1) and installed Poweramp. I have used a third party theme on my previous phone (It's the material one), I have installed it to the P9 as well, but actually I can't see anything from third parties in the themes list. (Tried it with the official HD themes, too.)
The other ussue is related to the EMUI I think, the track info and the controllers are black on the notifications list.
Hoping to fix it very soon, this is my favourite music player, using it for 4 years!