It finally works!
I have downgraded the Deviation Firmware to 5.0.0 and now it works.
Even better: it works with a CC2500-module salvaged from a MJX-F645-Transmitter,
and it also works with a module from aliexp. with PA and LNA...
So now I'll have to put back together the MJX Transmitter...
...after some maidening with my K110...