Does KJ-600 even use new engines? Most people on Weibo seems to say it still uses WJ-6C. Also there is a 5000kW turboshaft under development so no need to convert turboprops into turboshafts.The reason they use low power turboshaft engines is because these are what is available in China right now. This is good enough to figure out the problems of making a tiltrotor in a prototype.
But you already have the carrier AWACS aircraft KJ-600. Their turboprop engine converted into a turboshaft should have the power level for an Osprey sized aircraft.