We'll require you send us isolated stem files [preferably in a high-quality .wav format] for mixing. Please send two versions of your session; one with all effects and all with zero effects - this gives us a feel for your vision.
Assuming that your mixer has done a stellar job, please arrange to send us a final .wav mix for us to master. Reference bands, songs etc are required. Otherwise we'll make your metal band sound like Bjork.