While the EW-65 upgrade card is a slightly different configuration than the EW-01, 02, 03, and 04 cards, the connectors for all five cards ARE THE SAME, hence all of them fit the two connectors provided in the KN6000. It doesn't matter which card is plugged into which plug-in slot because both are identical, thus there are no compatability problems. It is easy to remove the screws from the back of the instrument and insert the cards. All you need is a Phillips screwdriver. Installation instructions come with each card as well as a list of the sounds.
Since you play in pianist mode primarily, my personal opinion is that you would be very happy with the Concert Grand sound of the EW-65 upgrade kit. As I said, I have the EW-01, 02, and 03 cards and currently have the 03 installed. The 03 card has "Vintage Keyboard" sounds. Since it is the only one of the three cards that has piano sounds (all electric piano), you may be more interested in it than the others. It also has a wide range of organ sounds and I like to play piano and organ, hence the reason I have the 03 intalled in preference to the others.
Well, I've rambled on long enough. Hope these additional comments are helpful. Take care.