We present theoretical models for populations of low-mass X-ray binaries in two elliptical galaxies NGC 3379 and NGC 4278. The models are calculated with the recently updated StarTrack code (Belczynski et al. 2006). StarTrack is a state of the art population synthesis code that has been tested and calibrated using detailed binary star calculations and incorporates all the important physical processes of binary evolution. The simulations are targeted to modeling and understanding the origin of the shape characteristics and the normalized number of sources of the X-ray luminosity functions (XLF) in these galaxies. For the first time we explore the population XLF down to luminosities of 5x10E36 erg/s, as probed by the most recent observational results (Kim et al. 2006). We explored the parameter space running models with different common envelope efficiencies, stellar wind prescriptions and initial mass functions. We were able to find models that produce an XLF in excellent agreement with the observations both in shape and number of systems at a specific luminosity. We also find that the treatment of the outburst luminosity of transient systems remains a crucial parameter for the determination of the XLF as the modeled populations are transient-dominated.