larigot, in addition to what Fran has indicated you can use the B4fx as a VST insert/send effect within a host such as forte Ensemble to turn on Vibrato, Overdrive, etc. Furthermore, you can turn on rotary speakers (up/lower, slow/fast) by sending midi control messages (Appendix B Page 62). So in the A37 you can program midi messages and store them in one of 128 memory locations.

Similarly, you can change drawbar settings very quickly sending patch changes from the A37 to the B4. It may not be quite as good as the continuous drawbar changes in real time with a real B3 - but it is very good. If you want to get fancy you can always send continuous control changes using say 9 instances of the B4 DXi from the A37. As I mentioned previously you can setup scenes within host software such as forte Ensemble. These setups can include anything from volume to other controller changes. In fact, it stores the current B4 setup as a scene.

So you see you can get very close to the real thing. Nothing is perfect but it is very good indeed!!! For those who must have the real deal I always say well then buy it....Hammond B3, Violin, Guitar, Sax and so on. It is very difficult to do an exact replica of the real deal with todays technology.