Well, the other option is to use a fully-featured controller, and map the style controls, etc., to the pads and sliders of the controller. I think DonM had success pairing a Roland A80 with the BK-7m using this approach.

When a manufacturer makes the decision to release a module, having pretty much any function that any player might need available via MIDI is super-important. (IMO it's important for any arranger or synth, period!) I think the BK-7m scores pretty well in this regard.

I agree with Paul's observation that the Audya module is huge and would be awkward to place above a keyboard. I have little experience with Ketron products, so I can't say how good their MIDI implementation is, or whether that approach would work.