Only problem with adding a second keyboard to a Tyros is, it only mirrors certain things. It's not like it is a completely programmable independent, splittable manual. I think you can get one extra sound, or NTA on the lower, but, if you use a dumb controller and expect the Tyros to store all what you want in the Registration, it falls a little short.

Better than nothing, but for organists using some of the better home organs, you may find it a tad restrictive. It's a shame, really, as it is ONLY software that needs updating to achieve this. If enough people clamor for it, PERHAPS Yamaha might consider an OS update?