I have both in my living room. And you know what, it's a tough choice. I would go with the 2000 for these reasons:
Styles have 4 variations, and there is a Break available. This the BIG difference.
It's lighter in weight.
The 2000 allows more control and easier access to microphone settings. It includes Noise Gate and Compressor-Limiter.
The Vocal Harmonizer is easier to access and control.
It has the Cool EGuitar and Vintage Guitar sounds that are really great. The Pedal Steel sound is much better on the 2000.
The operating system on the 2000 seems to be more stable and reliable. I experienced quite a few glitches on the 8000. There was a problem with the effects on the voices not always changing correctly with the Registrations. Nothing serious, but annoying.
I like the keys on the 8000 a little better, but not very much difference.
Although the 8000 will accept a hard drive, I never put one in it. The 2000 is faster reading the floppy. The 2000 also reads the floppy faster than the 9000 did.
I really like the "copy and paste" functions on the 2000. The entire keyboard is easy to learn and use.
The sampler in the 8000 would be a factor if you needed a sampler. I only used it as a gimmick.
The sequencer in the 2000 is much improved.
Hope this helps. If you have specific questions I will try to answer.
DonM