Yes, Opeth is familiar to me a bery progressive death metal. And as I read on Spotify an ex Opeth member, Martin Lopez was a guest amongst other in one Amorphis album.

I didn't know Symphony X, as I listen just now, it's also a progressive band. The keyboardist is a virtuous (the guitarist too, like the Dragonforce guitarists). The lead vocalist voice is between Ronnie James Dio and Miles Kennedy. I put thimese bands to my following list, thx!