I have a PSR740 and gig it together with a Hammond XM-1. I can't say how this compares to the B4, but it does give you a real box you can kick and drawbars you can pull, sound is pretty good too. I also have a Hammond T-500 which is their last tonewheel organ and the XM-1 compares favourably, but doesn't have that nice smell of warm oil after an hour or so!

The PSR740 isn't the ideal master keyboard because midi configuration data is not stored as part of the user presets. The best way I have found so far to have access to both PSR and Hammond sounds is to dedicate R2 setting to drive the external module and mute R2's sound in the PSR's mixer. Anyone have any thoughts on this?

The PSR's own drawbars are OK and an improvemnet over the PSR8000, but not in the top league. Sound 40 (electric organ) is also useful for some things.

Good luck

Paul