Scott,
I just received my brand new Roland A-37 and it works great! I can now control my Tyros with the left hand and, at the same time, either my Motif ES rack or my Roland Fantom XR with the right hand (I can even layer the sounds from both the Tyros and one of the modules).
The funny thing is that now my Tyros sounds better than ever, because the A 37 has different velocity curves, that apparently squeeze out of the Tyros every bit of its sound. Not to mention the wider keys (they are not as pleasant to play as the G 70, but for 500 euros what can I pretend?)