With the exception of the Yamaha PSR-2100 having a better vocal harmonizer function the Technics KN6000 is a much better instrument. The features the KN6000 has that make it superior are:

A nicer feeling keyboard with aftertouch (PSR keyboard feels very cheap in comparison)

Better sounds overall (Soloist sounds are great)

A sequencer that's quite useful (Yamaha's sequencer is a toy in comparison)

More extensive style editing features

More extensive sound editing features

Synthesis features for creating entirely new sounds

Tracker ball with real time control functions. This is especially useful for filtering sounds or doing pan and FX control in real time.

Expansion board capability (2 slots)

Hard disk capability

Better build quality

FLASH based software for updating

FLASH based sequencer memory so you can record a song without having to worry if a floppy disk is loaded into the drive. Sequence files stay in memory for around 90 minutes so if you accidentally shut the KN off, you can power it back up and your sequences will still be there. Even the flagship Yamaha's do not have this feature.

Large Color LCD screen that's very easy to read and fully adjustable

Slide Show capability

More intuitive user design with more dedicated buttons

A sound system that's among the best of any arranger keyboard

If you already have a KN6000 I'd suggest keeping it and adding the EW65NX expansion board. That's going to give you lots of new sounds which include a new Grand Piano, many new Soloist woodwinds and strings, and most of all new Live Drum kits that are much better than the stock KN6000 drums.

If you absolutely have to have Yamaha sounds buy a Motif rack and trigger it from your KN6000. This way you'll have the best Yamaha has to offer along with a great arranger, your KN6000.