I think the majority of issues with the 5x are from people who migrated from the 4x. There’s still a lot of 4x features that haven’t been added yet, and considerable trouble migrating data from the 4 to the 5. Plus some of the innovative 5x features are not well integrated into the Songbook yet.
Opinions are almost universal that the sound quality of the new arranger is a very big leap forward (the big increase in the number of insert effects and quality of the D/A converters have imho achieved this).
If you don’t need to import a bunch of legacy sample data from a 4x (or 3x) and if your arranger experience is fairly basic, you don’t use a lot of custom samples or do a lot of bespoke style creating and editing, you may find yourself very happy with the 5x. That’s the reports from most first time Korg arranger users… most of the dissatisfaction from people who got used to the 4x’s features (like style creation from SMF’s) and used a lot of the more advanced features.
No doubt you’ve been to Korgforums.com, the main PA arranger users group. There’s definitely two factions, those who mostly got a 5x by getting rid of their 4x, and most of them aren’t happy campers, and those that came from Tyros or Genos or from Roland or Ketron (and a few that the 5x is their first arranger), and most of those are ecstatic…
I guess you need to define pretty carefully what you want to do with your arranger - Turn it on and just play with the ROM styles and sounds, or if you want to use or create custom styles and sounds. You may have a very different outlook depending on these.
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An arranger is just a tool. What matters is what you build with it..!