The initiation of straight breakdown paths has been identified as the key issue of the LIB propagation channel formation scheme in the HWIFR dense atmosphere. Straight preionization trails have been suggested as means for guiding the breakdown along the designated beamlines. A multi-group Boltzmann equation solver has been constructed for estimating the capability of several preionizers to induce such trails in dense D2O vapors. A new approach capable of predicting the steady state streamer wave shape is used to estimate the minimum conditions for launching a streamer in the preionized path. The electrical resistance of the trail during the streamer propagation is evaluated with a simple one dimensional routine. Finally the transition of the streamer-induced ionized filament to a multi-kA-carrying plasma channel is simulated with a modified radiation MHD code. Other results of this study, including the determination of the preionizer intensity and the minimum applied potential required for the initiation, are presented in this paper.