Actually the 777-300s used to have Trent 892s but when they were derated to 84,000lbs of thrust, the engines were technically no longer Trent892s. A new designation was given to the engines that CX operates which are unique in that they provide only 84,000lbs of thrust for take off, but then as the aircraft climbs into higher altitudes where 84,000lbs is not enough to keep a good rate of climb going on a max weight aircraft, the engines slowly increase their thrust rating to 92,000lbs.
The designation by Rolls Royce for these engines is the Trent 884b.