The drum peripheral on rock band only has 5 inputs (bass pedal, 4 tom-type things). Axe and Martin sound like they have six arms!
Honestly if they can put the beastly Neil Peart and Keith Moon in there, they should have no problem with Axe and Martin.
3 things I'd like to point out after reading this thread 1) Rockband has 2 different drum sets, the basic drum set is a cheap 4 pad one pedal kit. the premium kit is customizable, full metal adjustable frame. mine has 4 pads (snare, two toms, floor tom) 3 cymbals (high hat, ride, crash) and two kick pedals. 2) I started listening to Opeth a year ago, and I don't find Orchid or Morningrise boring at all, I think those two CD's are crazy and amazing. My favorites are Blackwater Park and My Arms, Your Hearse, my least favorites are Watershed and Ghost Reveries. 3) Rockband has plenty of metal, they releases new songs for download every Tuesday (Thursday for ps3), current track list is like 580 songs and they are releasing a full album from Stevie Ray Vaughan this Tuesday. Metal / Progressive Bands in Rockband Abnormality All That Remains Anarchy Club At the Gates Avenged Sevenfold Black Sabbath Black Tide Breaking Wheel Children of Bodom Crooked X Devil Driver Evile In This Moment Iron Maiden Judas Priest Killswitch Engage Lacuna Coil Lamb of God Machine Head Mastodon Megadeth Megasus Metallica Mötley Crüe Motörhead Pleymo Ratt Static X System of a Down The Haunted Testament Under Oath White Zombie X Japan Yngwie Malmsteen's Rising Force Between the Buried And Me Coheed and Cambria Dream Theater Jethro Tull Kansas Rush