I have the MP3 player you referenced and it works like a charm.
Although I do not yet have a KN7K, I have downloaded styles from the Technics website and transferred them to the SD card and then used them in my dealer's KN7K. I have also verified that the MP3 audio files play back through the keyboard.
I have been wondering if there are any functions that cannot be performed with this unit as opposed to the reader/writer kit with Jukebox sold separately by Technics. So far, I have found no limitations at all and think this MP3 player with its included USB reader is a good deal.