With regards to the Kronos APs/EPs you really should play them on a weighted action. I noticed this in the audio demos prior to getting mine. I was really only knocked out by the APs in the Japanese demos, which were done on weighted actions. All the other demos were on the 61. With the semi-weighted action you grab into the velocity layers too high and it's too easy to push them to the extreme. In my home studio I have a semi-weighted and weighted action placed like a dual manual keyboard and I am frequently shocked at the tonal differences when playing a sound on one of the keyboards and then moving to the other. It can be stark.
If you’re playing the Kronos 61, try going into the main piano parameter page and setting the VELOCITY INTENSITY to +30 to +60. This will significantly increase the dynamic range. While you’re there you might take the VELOCITY BIAS down a bit, maybe -5 to -10 and possible lower the lid a bit.
I recommend you try setting the Velocity Curve in Global to 9 on the 61 as well as the 73 and 88. It makes for a more expressive playing experience, IMO.
Still, I believe something psychosomatic occurs when you play an acoustic piano sound on a semi-weighted synth keyboard. There is a disconnect between the sound and the feel of the action, so your brain says something is wrong or phony. Play the same sound from weighted keys and it sounds/feels much more authentic.