Hi to all,i have had experience with all the korg keyboards and many different brands external units,the korg pa3x and pa800 are the best at the moment also what i found with the ketron very good clean and great compresson effect the only thing that lacks on the ketron and dont forget very important is user scales that ketron dont have on there arrangers where all the balkan country's use alot,as for yamaha i have never had any experience with