RE: JR10x to DSMX
Then the online X9503 manual Horizon has on it's website is an old pre-DSMX one because it does not mention DSMX mode. I did see photos from a seller which shows an X9503 with the DSMX logo on the face of the TX as well as a DSMX indication on the LCD screen.
I was most worried that getting a DSMX transmitter would obsolete my stash of DSM2-only receivers.