Hmmm, let me make two different groupings here:
Vocals: Zach De La Rocha (RATM) & Serj Tankian (SOAD)
Lead Quitar #1: Tom Morello (RATM)
Lead Quitar/Rhythm Quitar #2: Davor Malakian (SOAD)
Bass: Jim LaMarca (Chimaira)
Drums: Tomas Haake (Meshuggah)
The reasoning behind the group: I'd love to mix the Rocha-Morello and Tankian-Malakian pairings together, I feel they could do incredible music even if they had two vocalists and two lead quitarists. LaMarca can push out some feasible heavy metal bass lines, and I believe he'd be at home with the style of the group. Tomas Haake is known for Meshuggah, which is a more hard-line band than any of the others, but Haake is so incredibly talented I honestly think he could drum for any band in the world.
My other outfit:
Vocals: Marcus Bischoff (Heaven Shall Burn)
Lead Quitar: Scott Hull (Pig Destroyer, Agoraphobic Nosebleed)
Bass: Stefan Westerberg (Carnal Forge)
Drums: Mick Harris (Napalm Death)
First of all, Marcus Bischoff. I swear he delivers some of the sickest vocals around outside of Obituary and Meshuggah's Jens Kidman. His voice isn't the normal growling or barking of death metal, but rather it's this painful-sounding semi-scream, semi-growl that is just mindboggling if you start actually thinking about it. Scott Hull is one of the greatest grindcore quitarists still doing music today, and PxDx and ApNb speak for themselves. Westerberg hails from Carnal Forge, which plays extremely fast thrash/death metal hybrid, and would fit right in with the other speed freaks. Mick Harris... The man's nickname is/was "The Human Tornado". Think about that.