If you listen to any live music recorded in a large venue then I think you'll love the scale and depth that a good sub adds. My Sub (a rel strata) also adds considerably to 70% of my studio albums, but the live recordings are where it really knocks your socks off and makes you feel like you're really there.
I'd start with a single powered sub (such as REL, ACI or Vandersteen) and place between the main speakers, and slightly out into the room, so as to give good room loading, and minimal directionality to the bass.
I'd start with a single powered sub (such as REL, ACI or Vandersteen) and place between the main speakers, and slightly out into the room, so as to give good room loading, and minimal directionality to the bass.