Could you please help me out with this... Do I need the additional "Breakout Box" to connect my studio monitors via XLR?
No, at least not at first. If you only hook this up once to home studio gear and never move it then the BoC will probably be fine.
But if it's anything like the BoC for the original Duet, it might not hold up to the rigors of playing out live. Worse still, it's a one-of-a-kind BoC, so the day it fails on you out in the field you'll be SOL.
IMO, the BoB is easily worth the additional $80, though I'd prefer to at least see it come with a backup proprietary cable (to go between the Duet2 and the BoB) or to have them sell the proprietary cables online as an accessory.
At least the TSoundPro BoB
for the original Duet offered additional cables -- and you could mod one from a stock 15-pin VGA cable with a pair of needle-nose pliers in a pinch. Not that you'd need to, those cables were durable as hell. Unfortunately, the pictures I've seen of the Duet2 BoC and BoB cable so far both look like they are made with the same dainty-gauge wire as the BoC for the previous Duet.