we're about to add a second guitarist and i'm currently using a dual rectifier. as he's getting ready to upgrade his gear, what would complement a dual rectifier: another one or a mark IV.
A Mark IV or Stiletto would compliment the DR more than another DR, for the most part. There's always exceptions, like completely different sounding guitars and one using el34's and one using 6l6's, but for the most part I would say Mark IV or Stiletto.