Amelio,
1- the ideal setup would be to use the Motif 7 as a master controller and the Tyros as a slave, because this would enable you to make full use of the 76 keys (they have also a better feel, compared with the Tyros' own keys). At the same time you could also create your own performances on the Motif -in split mode- and layer them with the Tyros' internal sounds. I too have been thinking of a solution like that; my idea would be to use the Motif arpeggios together with the Tyros styles, setting the Tyros clock to "master" and the Motif to "slave".
2- Another option would be to use a different 76 notes controller, like a Fantom X7 or the Korg PA1X-pro or even the new Roland G70. But, all in all, I think that the Motif blends better with the Tyros, sound-wise (they share many sounds and also a similar effect section).
I will wait a few more weeks, then I will compare all the keyboards available and make my own choice.
Ciao!
Andrea