When you download the Firmware you always find a pdf called How to update your KPA.pdf. This description recommends to put the kaos.bin into the "OS Update" folder. And this procedure does not need the thing with hold both '<' and '>' keys.
Quote from wiKPA.pdf, page 18INSTALL OR REINSTALL THE FIRMWARE
- Switch the main knob off
- download the latest KPA firmware
- use your usual KPA-formatted USB stick
- copy the unzipped firmware file kaos.bin into the root folder of the USB stick (NOTE: there must be no other copy of the kaos.bin file elsewhere on the stick)
- plug the USB stick into the KPA
- press and hold both '<' and '>' keys
- switch KPA to tuner while still holding both keys
- something like 'booting and installing' will be displayed
- wait until the firmware is reinstalled.
This is a kind of forece install of Firmware. And here the kaos.bin should be put into the root folder.