I think they'll be able to win in 6. With the rotation pairing down to 8 or 9 (TA, Finley, Sheed and Baby), I think our offense will be better and we won't suffer through as many of those horrible offensive lulls that spot crappy teams leads or keep games close.
Miami is a poorly constructed team. They only have 2 good 3 point shooters in their rotation and only one of them starts, and they have flawed/aged wannabe stars like Beasley and O'Neal in place of good role players. They will have real problems guarding KG with Beasley (KG averaged 19-7-5 on 77% shooting in his 2 games against them) and Rondo with Arroyo/Chalmers (Rondo's averaging 20-4-11 on 58% shooting in his 3 games against them) and the slow O'Neal trying to help and recover.
Still the Heat crash the boards pretty hard, Haslem can give us problems with his effort/mid-range J/rebounding and Wade is a nightmare for Ray Allen/Pierce. I'm sure Q-Rich will burn us from deep a couple nights too.
Unfortunately the C's chances at 2nd round triumph appear to be virtually nil, unless Shaq returns to the Cavs and slows them down to our lethargic pace.