The simple answer is the Roland Vk-8m Drawbar module:
http://www.rolandus.com/products/details.asp?catid=10&subcatid=42&prodid=VK%2D8M

The Tyros organs do NOT sound like a NI B4 NOR do they sound like the XK2. The VK-8m, on the other hand does and in my opinion playing live it surpasses many sample based and other lower quality Hammond Simulators. I did a study of all available products on the market and the VK8M, although it does not match a real Hammond or Leslie, is the next closest thing.

The VK8m features real drawbars, Tonewheel emulation, Vibrato, leslie, has the D-beam, controller, and is fully tweakable.

Plus it has buttons to trigger presets.

I play live with a Tyros and a Korg Triton Extreme, and for my personal taste, the VK8M blows them both away. I'd rather have an A-100 with a 122, but I'd rather gig with this baby any day.

Al