I think if you want more speed or range selectable speeds, then you're going to have to go your own way with it. I've not seen Syil offer anything other than changing to the X4 motor and controller. Offering is one thing, getting is another...but that is a different story.
Others have run standard bearing up to 6000RPM and not reported any significant wear or heat issues. There are some "high" spindle threads on here where people have used different bearings.
I'm at the design stage of changing to a standard AC motor and drive it with a VFD. The main problem is that there isn't a lot of room on the top of the SX3 head and distance between pulleys isn't large. Getting a stepped pulley for two speed ranges to fit is proving interesting, but should be just about doable.