Hello.
I don't think the difference with Audya is only about sound quality. Ketron has always had very good sound quality which was never lost. Event is, I think, the most creative Arranger ever made. Its creative possibilities are truly unique, since we can have User Real Bass (audio), User Real Chord (audio), User Real Drum (audio) with 3 different Percussion sliced Groove section and two different midi Drum kit section.

Noteworthy is the new midi multichord which is a new Ketron revolution and we can have in each different chord (for example Major) 7 or even 12 different midi files, the same in minor, m7, 7, 6, m6 and so on respectively. The same in midi bass as Multbass. Apart from that we can have simple user midi file chord as well as user drum midi patterns in each style and in each variation separately! For the first time in Ketron we can also have a different time signature in each variation (like Korg), which is equally important.
Also extremely creative on stage is the new real-time FX section, from which through switches and rotary switches we can control the FX, open and close, change the FX algorithm, as well to have control over predefined parameters. As if we had external FX pedals.
Two different Voice section, with different sliders.

New Natural algorithm in the Voice Edit (with OS 1.3) which adds a random delay (1-50ms) to each of the three sounds of each Voice which makes the combination of instruments, e.g., saxophone, trumpets, accordion extremely more realistic because in a real orchestra it is never possible for all three of these instruments to play and sound exactly at the same time, at the exact same point in time but continuously in each instrument the timing is different on each note even though they play together.
Excellent!!

I could list more but they need more explanation and I don't want to confuse you. I am lucky this time to have in my studio the three top models of all companies: Yamaha Genos, Korg Pa5x, Ketron Event. Each of them has its positives as well as its negatives. But what I can tell you with absolute certainty is that the Event is the most creative (especially in the creation of styles) that has ever been made. And since you're an Audya fan (as I am), listen to this demo of what an Audya style sounds like through the Event. Believe me, I don't want to go back to it (to Audya that is) even though I have two Audyas (Audya 76, Audya 5) and they still work flawlessly!!

Audya Style convert to Event demo https://app.box.com/s/ovs1dg6lhq8ilrjix8yaev570l8f19b7

Also here I have a small with the same song (a Greek song), demo so that you can see how a Pa5x style (and Pa5x in general) sounds versus Event. It's not a representative sample, but you'll get an idea https://youtu.be/BxvO1e-bOhI