Beaky, I am not sure that controller will do what you want, ie., trigger a Fill. That function is not mentioned on the features listed.
A simpler way is setting up one of the foot pedals to trigger a Fill, use the other foot pedal for your "Harmony" and to get a sustain effect, (I assume you are using the sustain with the Grand Piano voice), just turn on the 'Sustain' button up at the top under "Voice Effect". Although it is sort of a pseudo-quasi sustain effect, it does at least provide some sustain functionality.
To get a more thorough and optimal sustain effect is to use the foot switch of course. And using both the foot pedal AND the Sustain button for sustain produces an even better sustain effect imo. But that's beside the point.
If you can "endure" just using the 'Sustain Button' as I mentioned, then great. If you can't and need a permanent, ie., "better" solution, try the midi controller and if it works, great, if not; if they have a 30 day return guarantee, just return it for a refund.
I am also waiting for an Arranger that will have 3 foot switch inputs like the Tyros has, but one that will also have built-in speakers. With Summer NAMM just a couple months away I am hoping there will be a new Arranger or two that will have both of those features plus the other features on my wish list.
There are too many to list at the moment but someday my ship WILL arrive.
And for all it's worth, I hope Yamaha is the one it arrives on
. Yammy is the best when it comes to being able to accumulate all those fantastic Styles from the Net. Literally thousands upon thousands and ten thousands upon ten thousands. Or as DonM would say, "A whole heap of them".
Just teasing Don! Any way Beaky, I hope you find a workable solution.
Best regards to all,
Mike