I've not had a chance to play the KN2400/2600 but if they utilize the same sound set as the KN7000, they'll definitely be worth considering. Personally I find Technics to have better, more realistic, more natural sounds than the Yamaha arrangers. Many of the Technics sounds use more ROM memory to make up the sounds and have built in nuances that add something unique. I used to own a fully expanded Yamaha 9000 Pro and while I really liked a lot of its sounds, I tried out a KN7000 and was far more impressed with the KN7000's sounds and features.

One major downside of Yamaha arrangers compared to Technics is the sequencer and style creator is inferior. The Technics sequencer and style creator is quite frankly easier to use, more intuitive, and allows for much more complex editing than Yamaha arrangers. The KN's also allow you to do more editing of sounds than the Yamaha's allowing for a greater sound palette.

Comparing the PSR-2000 and PSR-2100 to the Tyros or KN7000 is unfair as the Tyros and KN7000 do sound better and have more features. Still the PSR-2100 will give you most of the Tyros sounds and features for a lot less money. If the Technics KN2400/2600 fall within the same price range as the PSR-2100 I would suggest you take a serious look and listen to them as I find Technics to sound better and the build quality will likely be better than the PSR-2100. Yamaha does make some decent sounding keyboards but their lower priced products suffer from poor build quality and cheap materials.

In regard to sound demo's ... never judge a keyboard by a demo that the manufacturer came up with and put on the NET. Play and hear the unit yourself so you can truly see what it is and isn't capable of. I've found many online factory demos really stink and yet the product was quite good when I heard it in person. Perhaps some manufactures don't see the benefit of having a good online demo but some companies like Yamaha do and they spend countless hours producing great demos to woo you. Don't let the smoke and mirrors get in the way and judge for yourself.