  We present a precise isospin analysis of the B -> Dbar(*) D(*) K decays using
new recent experimental measurements on these final states. The decays B ->
Dbar(*) D(*) K, originating from b -> c cbar s transitions, are linked by a
rich set of isospin properties. The isospin relations that connect the decay
modes are presented and a fit is performed to obtain the isospin amplitudes and
phases. We discuss the results of the fit and present a new measurement of the
ratio of branching fractions BR(Upsilon(4S) -> B+ B-) and BR(Upsilon(4S) -> B0
B0bar). We finally discuss the implications of our findings for the measurement
of the unitarity matrix parameters sin(2 beta) and cos(2 beta) using these
decays.
