Hi Mau Van, I also added a Korg keyboard to play styles with the PX5. I'm using a Korg microarranger which has the same sounds of PA50SD or PA80. It has only 32MB of rom samples but guitars,strings,sax,accordion are amazing. The analog drums are also impressive. However I like better the piano of the PX5. I can fully control the arrangement chords with my PX5 keyboard (by midi cable). I really like this setup. I agree with you that CASIO should improve some of the "classic" sounds (guitars and string). Overall, I'm very happy with the PX5 because of the EQ, piano sounds, keyboard action however I definitely see room for improvement.