Not so different as to not bait other members about gear, LOL.
Donny, the BK-9 is a completely different beast to the BK-5. There's a lot more shortcuts for navigation, and there are four switches by the bend lever that can do most of what you might have missed from the front panel, plus an FC-7 input for 7 more functions immediately available.
Not to mention that the iPad apps make navigating and editing a breeze.
I have spent quite a bit of time on the BK-5 (friend had one and a BK-3, and I still have my BK-7m) and you can trust me, the BK-9 is a completely different beast. There's no way I would be so positive in my reviews of it if it had the same shortcomings that the BK-5 does. The action is FAR superior to the BK-5 (mind you, as an S950 owner, obvious that has no impact on your buying decision!) and navigating and operation are MUCH, much easier.
Not that you will be the slightest bit interested even if it was completely different, but it is!
You know how much I like the G70. With the iPad apps, the BK-9 is all likelihood going to replace the G70 for all but the most critical gigs I do (playing strange music with a strange band, and no advance warning as to what setups I'll need), and I have a feeling once I have the iPad and learned that well, it may end up totally replacing the G70 in the end.
I would definitely NOT be saying that about the BK-5.
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An arranger is just a tool. What matters is what you build with it..!