There are a lot of panel functions that don’t get MIDI codes, and some manufacturers (I’m looking at you, Yamaha!) make the job of replicating standard functions MUCH harder by using sys-ex instead of standard PC/32/00 codes, which limits your choice of controller, not to mention making the job of mapping a lot harder.
If you are content with basic control, sure, it’s doable. But things like BassInv, Reset, Accel/Decellerando, Chord Sequencer controls, things like that are often left with no codes and have to be reached for on the module. Although they can be mapped to an FC7 switch with a BK7-m, many things have no MIDI code.
So you end up with the double whammy of having a ton of quite complex programming to set up all the controller’s top panel controls, and STILL having to dive a long distance for the module’s own buttons that have no code, because you can’t rest the module on the controller..!
It doesn’t really make much sense if you play a keyboard… Even if you want an 88 piano weight arranger, personally, I’d get a dumb no controls 88 and put the 76/61 right on top, B3 style. A lot of sounds (organ, clavinet, synths etc) are easier played on lightweight plastic even if the pianos and Rhodes’ are better with the weighted 88.
But for MIDI accordions, MIDI guitars, horn players etc. who aren’t playing much if any keyboards at all, perfect. I only use my BK7-m with my keytar, it’s brilliant for sitting in with full bands etc, but I’m not using the style section with those!
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An arranger is just a tool. What matters is what you build with it..!