I have owned SPK kaos and pro. SPk kaos has 2 layers of padding in the tongue and heel vs SPK pro has 3 layers in tongue and heel. SPK pro has a leather cover and a rubber grip thing between the heel and toe pads. I'm pretty sure the boot plastic is the same on booth boots I think Salomon just added a few more rivets to the pro's cuff to firm the boot up some. If you got he extra money get the pro or get the kaos and spend the extra $100 on some Intuition Full Tilt liners.
I have never put a Intuition liner in an SPK. But I had some in a pair of Salomon 1080 Foil boots for a few seasons til the shell soles got too worn out. The Full Tilt liners worked great. Don't see why a Full Tilt liner wouldn't not work with an SPK shell. Go and see a boot fitter first.