WARNING: Once GCC system is upgraded to firmware 1.0.3.x, downgrading to 1.0.1.x is not allowed.

GCC6010 System Firmware 1.0.5.6: Release Notes    Firmware File

GCC6010 PBX Firmware 1.0.27.14: Release Notes    Firmware File

Note:
Starting from GCC system firmware 1.0.3.5, a single complete firmware file gcc601xfullyfw.bin can be used for upgrading GCC system and PBX module. The single complete firmware file can be downloaded here:
Release GCC601xFullFW Sys-1.0.5.6 + PBX-1.0.27.14