BETRAYING THE MARTYRS
Make Them Suffer is a band that fits in this requirements, although they have started with a sound closer to deathcore, they have very elements produced through keyboards and their latest works are Metalcore without a doubt.
The Within Temptation band also employed symphonic elements, but i think they're don't classified as Metalcore, the their music fits in the metal symphonic form.
Epica is other that shows similarities with opera and so they can enter this.
Mechina is prog metal, but they are used to put gutturals in their songs.
Worth to test and know these bands.
