The last free upgrade from Korg for my PA1X was this

Korg Pa1X OS Version 3.0 Released
February 15, 2007



The Korg Pa1x arranging keyboard workstation series has gotten a fresh operating system version and with it a notable expansion of capabilities. Version 3.0 is for Korg's Pa1x, Pa1x Pro and Pa1x Elite. The upgrade also ships with a new set of piano sounds and 64 new styles. Here's the main upgrade feature list:

Support for long file names. You are no longer limited to the classic format 8.3, all capitals. Now names can be as long as you like, and mix upper and lower case characters. Names of files transferred via USB or CD from a personal computer will not be cut into shorter names, and will look exactly as the original
Easier way to start recording Songs from any measure. Go on recording your Song. If you want to do second-pass recording, starting from a measure different than the first one, you are no longer asked to move to that measure using the Fast Forward command. Just choose the new starting measure with the Start Measure parameter, and go on recording from there
Up to 16 oscillators per Sound. Create Sounds as sophisticated as you like. In the Pa1X, each oscillator is a different sound. You can either create very rich sounds, or add as many dynamic layers as you like, for the highest degree of nuance in a single sound
Smarter pre-selection of Style Elements. You can now select a different Variation just before jumping to a different Style. The Variation you choose will overtake the one memorized in the Style Performance
Faster SongBook operations. Huge SongBook files are now loaded and saved much quicker
Ending 3. A new, shorter ending is included. For those of you who prefer to cut short in the end
Revised user interface, with bigger buttons, bigger fonts and colored sliders
Enhanced Lyrics and Select pages, for better readibility
Revised Musical Resources, with various improvements and the new Ending 3 for Styles
Smarter Solo Mode, to be activated with Shift + Touch
Tempo Lock in Song Play mode, to quickly freeze Tempo and keep it the same in subsequent Songs
Contextual Help now available also in Dutch and Russian languages

I can tell to that the upgrade was like having a new keyboard but i did not have to pay for it !!!

and it was major. The pianos were a major improvement, the sequencers was even more detailed and the ability to have asound composed of up to 16 elements blew my mind.