I think they are probably the exact same receivers, they are most likely just software limited. I wonder if you could upload the 6100 firmware to the 6050 and it would unlock the 10 extra watts of power and the THX Certification... They both draw 635 Watts and the rear and front panels are identical.
TX-NR6050 (Costco)
TX-NR6100
TX-NR6050 (Costco)

TX-NR6100
