it was the ew65 card which virtually upgraded the 6k to 6k5 status. The 6k5 piano uses the same samples as the digital pianos and was more subtle and richer than the 6k main piano, which had a stereo sample but did not have velocity triggered stereo multi-samples for example.

It is all a matter of personal taste, and the 6k piano might still be better to stand out in a VERY busy mix, but for solo and general playing I would be amazed if anyone who was used to steinway sound would not prefer the piano in the 6k5.

the ew65 card should still be available and had a good collection of other soloist sounds (recorded with natural vibrato and extra wave rom) superior to the standard sounds in the 6k.