We extend a previously proposed spectral reflectance and transmittance prediction model for recto-verso prints to the case of multi-ink halftones. The model takes into account the multiple reflections and the lateral propagation of light within the paper substrate (optical dot gain) as well as the spreading of the inks according to their superposition conditions (mechanical dot gain). The model accounts for the orientation of the incident and exiting lights when traversing the halftone ink layers, which enables modeling the measuring geometry. The equations for the calibration of the model and for the predictions are presented in detail. Several experiments with inkjet prints show that the multi-ink halftone transmittance model is as accurate as the actually most performing reflectance models for halftone prints.