  We develop a (3+1)-dimensional hybrid evolution model for heavy-ion
collisions with dynamical sources for the energy-momentum tensor and baryon
current. During an initial pre-equilibrium stage based on UrQMD, the
four-momenta and baryon numbers carried by secondary particles created within
UrQMD are fed continuously, after a short thermalization time, into a
(3+1)-dimensional viscous hydrodynamic evolution module including baryon
transport. The sensitivity of the initial conditions to model parameters and
the effect of baryon diffusion on the hydrodynamic evolution are studied.
