The radio can be switched between normal (PPM mode) and HSR acessing a small switch BEHIND the TX module.
In normal mode you can use after market Rx like LRP, NOSRAM, Novak etc or other brand Rx like Sanwa, Multiplex, Futaba (not PCM or Dual Conversion)
The Ko Crystals can be used in this mode, since they are intended for Rx with .455Khz internal frequency Rx and that covers all the Rx I have on the above list.
In HSR mode there are two options:
With the Ko 302 RX, with the TX configured for 2 channels
and digital servos, can be used in ASR
With this RX if you configure the Tx for 3 channels
the system will work in HRS mode anyway.
With other KO HRS Rx like the 301 or
with 3 channels
configured on the Tx can only be used with HSR
(like the Mars R).
Kind of tricky , but simple after reading the manual
PS: Confirmed with testing with Sanwa 311, Novak XXL and Multiplex Pico 4/5
There's only one more detail than Tom's post. And that's the number of channels configured. His post was absolutely correct.
Hope this helps