The Ultrasone sound is not for everyone, some love it but most do not care for it. I am one of the few ones who has enjoyed their sound and I have owned the PROline 2500 and the HFI-780. I hope one day to listen to the Ed8 to see if they would be for me, or not.
However, you mention you like the Grado sound. That being the case you could look for an used RS-2, which for certain music is IMO better than the RS-1. Another option would be an used SR225 which can be found for around $150 used. Personally I prefer the Grados out of a tube amp like the Mapletree or in some cases a hybrid unit like the old Musical Fidelity X-Can V2.
As I recall the Predator is on the warm sound and should help tame the Grado highly energetic top end. Good luck.