My tweaking is mostly done setting things up in the most convenient way for me to play live. Saving setups, making sounds and styles easy to access and call up, finding best styles for songs. . .
Almost all my changes in gear are made in the winter when it's too cold or wet to play golf or fish. Right now I'm in a major experimentation mode.
As for choice in keyboards, there are no bad ones. Tweaking is more necessary on Korg I think, but it's also probably the easiest to do it on, and it's one of the deepest as far as allowing the user to change every detail. Roland isn't far behind, if at all.
Audya sounds the best to me as far as styles and arranger parts.
Yamaha has great lead instrument sounds and a magnificent plethora of styles available.
Closest to perfect all around arranger for me remains the Korg PA3X, after you get it tweaked to suit you. I had some good reasons for letting mine go, but sorry I had to do it in many respects.
I'm trying to make the PA900 be a mini-PA3x. Jury is still out. BK9 remains in a solid place of contention. I have only a few days to make a decision! Whichever way I go, it can't be wrong!
I'm leaning toward the PA900 for the fact that it is pretty much an all-in-one package. Easy to transport, set up and play without peripheral gear of any kind except PA system. Not even that if the gig is small enough!
A perfect setup might be BK9 for bottom keyboard, PA for top, but that would be too much stuff to deal with as far as setup and transport.