Thank you all very much for giving me your opinion...

I am preparing a series of articles on my website. Each article will be an example of tyros configuration and a second keyboard.
eg tyros with juno 50 as a second keyboard or casio PX55 or Pa3X korg .
For each configuration , I give opinions , the pros and cons based on my experience or your own.
In my case : I currently own a tyros 4 , I also have a Yamaha digital piano that I use less and I have a lot of expanders , some are quite old (Roland jv880 , korg 01r / w ... ) .
The project of a second additional keyboard will help me to expand my sound capabilities , and have very different sounds, and why not : an additional 76 keys.
I will use the styles in tyros 4 , and the voices on the right hand , the 2nd keyboard gives me more sounds to play the melody with the right hand and also control all expanders .
As 2nd keyboard : I think about the Juno 50 and Korg pas3x (for 76 keys).
Or a Korg Pa800 associated with another expander Roland Integra 7