Don , and styles and sounds and internal speaker ...if u had to compare?

Nothing substandard about the PA 4X harmonizer. Don't know about the PA 900.

Is the soprano sax dnc on the pa900 similar sounding to the psr s970 sweet soprabo sax where when u hold the key down it expands and becomes louder

internal speakers I guive the nod to Yamaha s970


where the korg lacks is in the amount of styles available vs yamaha..there are workarounds, conversions, third party styles, create & record your own, etc if your willing to do the work for your needs,.....honestly you cant go wrong with either korg or yamaha at this point as we really dont have many arranger choices anymore like years ago....good luck

If you want decent harmony stay away from Yamaha. They don't even know what decent harmony sounds like. I produced a Cd with a rented PA 800 and the harmonies were good. The 900 took away one of the voices but I'm sure it's still good.
Here's one of my songs with the Korg harmonies.

https://youtu.be/wHgUfF9wDL4

God Bless,
Don

Sounds professional. Maybe adjusting the master comp/eq can make the s970 sound more closer to pa900. I was onlu using telmos eq settings... i forgot abt the master eq

Best tip for Yamaha harmonizer is to use the compressor and only use 1 harmony voice. It struggles with more, and needs the signal to be level to be effective. It's not awful, but it's close to the bottom of the pack of what's available.