Hmm. I dunno how things work on a Mac, but Rob does all his recording with his PC. The key point might be that he has an external mixing board he pipes his amp/mic/guitars/pedals etc through and thats then fed singly into the PC (I think), and then he adds layers of drum programming and synths using Fruity Loops or Buzz. Always sounds quite well mixed, but I'm not sure how he does it.