OK gents
thanks for all the suggestions, now I have some interesting suggestions . I will do a serie of articles on my website, to expose these suggestions 2nd keyboard for the Tyros.

1) Casio PX 5S
2) Korg Kronos
3) Yamaha Mox 8
4) Korg Pa3x

personally I would go for :

- sell my tyros 4
- buy a tyros 5 - 61 keys
- second keyboard : a pa800 or pa3x 76 keys
- this second keyboard will control all my existing expanders (roland jv880, korh 01r/w, proteus 2000)
- I will add later a roalnd integra 7
- and why not the ketron in rack ...

what do you guys think ?