Donny, I owned a Korg at one time, played it for about a year, then went to the PSR-500 because it sounded better than the M1.
I also tried to help a friend with his 600, which sounded just awful. He switched to the S-970 and both he and his wife were elated with the improvement in the overall sound. Regardless of the tuning, that 600 did not provide the sound quality of the S-970.
I'm not against any brand of keyboard - period! I have owned many, not near as many as but that's another story. I also owned a Roland for a while - never liked the way it sounded, especially the sax and guitar sounds, though the grand piano sounded pretty good when I tuned it a bit.
Now, I probably will not purchase an SX-900, mainly because my children and grandson are not at all interested in playing a keyboard. My son plays the guitar and uses my old 3000 for backing and a drum machine. My grandson plays the guitar I gave him for his 12th birthday (thanks Captain Russ), and my daughter does not play any instrument because she only has one functioning arm. Prior to her accident she was an accomplished clarinet player. I don't want to leave the burden of selling my gear to my children upon my untimely demise, which is the same reason I sold my sailing yacht for a fraction of its worth.
When it comes to arranger keyboards, to me, the most important thing is how it sounds. I can work with just about any operating system, though over the years I think I have pretty much mastered just about every aspect of Yamaha's OS. If the keyboard does not sound full bodied and realistic to me, it will not sound good to my audiences - IMO.
Unlike you, I never really had a problem with Yamaha's vocal processor. And, I rely heavily on my vocals as I am NOT a highly skilled musician. My vocals were my right hand and though I sometimes did some right hand fills, most of the time, I really didn't need them in order to sell the song.
Additionally, I really didn't need an arranger keyboard for midi files and midi looping - I rarely used a midi file during a performance of any length - just used a wide variety of onboard and third-party styles, of which, Yamaha has the most available and usually the quality is superb.
As stated in another thread, I really do not need a touch screen or tilt screen - it has never posed a problem indoors or outdoors. I performed a lot of outdoor jobs while in the Florida Keys, however, those jobs were usually in open sided Tiki Huts or under a small tent top to keep the dew from settling on the keyboard. There were nights when the dew was so heavy at sunset that it almost seemed like it was raining. If you were not beneath some sort of cover, you would be soaking wet.
So, if I were in your shoes, and in some ways I am, I would wait till I could get my hands on the SX-900 before purchasing. All the You Tube demos sound fantastic, but they are in the hands of some very skilled players. You are the guy who is always talking about road trips - why not take one to Frankie V's place and get some first hand information before plunging headlong into another keyboard. He has the Korg's in stock as well, so you can do a side by side. Hey, I thought you were semi retired - you can do this!
Gary