Jupiter,
I would be happy to give you my opinion about trading in your KN6000 for the Yamaha 9000 pro, but remember, this is my "opinion" and others might night agree with me.
In my limited times trying the KN6000 and KN6500 it has been my opinion in past models (5000) and in the current models that the technics sounds, especially drums are not as good as Yamaha sounds. Being that both of these are Japanese made, I've always compared these two the most closely and I've compared the Italian models including Solton, Generalmusic and Roland in their group. In the end though I realize they are all pro arranger keyboards. I have always thought that Yamaha and Technics have choosen to use Japanese Style creators where the other companys have used European. However, during the past year I have learned that this might not always be true. But, I will just compare the Yamaha and the Technics right now.
I like the Yamaha alot. It's piano, I think is much better and I think the rest of the sounds are generally more realistic to my ear. Yes there are some new solo orchestral instruments which are an improvement over the PSR9000, but generally it's the great feeling 76 note keyboard, the new vocal harmony XLR mic input and of course having 128 note polyphony is a real plus over the technics. Every 9000 pro owner loves their new keyboard and I've sold many in the last 2 months. I don't think you would regret trading in your KN keyboard for this one. I am in the US and don't understand British Pounds. Please tell me how much US dollars plus your keyboard you are spending so I can tell you if you are getting a good deal.
For speakers I hope you have the ability to hear and purchase in your country the new Yamaha YST-MS50's. These little beauties are a three piece set including two 20 watt satalite speakers and a 40 watt subwoofer. I hate to call them computer speakers, because people don't think they should sound as great as they do. I almost always sell a pair of these speakers when I sell any keyboard in my store, including Tritons, XP80's and all arranger keyboards when people need an extra 80 watts. And, the amazing thing is these speakers sell for $149.00.
I hope this helps
George Kaye