will any 75 mhz rx work with the JR XS3? I've got a couple futaba's I'd like to combine. If not, which will work?

Airtronics and JR receivers will work in FM as they have the correct crystal shift. KO Propo does also I believe.

Futaba equipment works with JR in AM but not FM

I don't know about futaba, but I know the Novak XXXL reciever does work with the 75mhz JR Xs3 Radio. It is the same type that you can change the frequency. If you have a few futabas why not just try it?

Anyways I'm interested to find out as I'm in the same situation as you are.

One more time -

The phase shift only matters for 75Mhz FM. All others are compatible. For 75Mhz FM, Futaba and Hitec are compatible since both use negative shift. Airtronics (Sanwa), KO, JR use positive shift. You can't mix Futaba and JR if you're running 75Mhz FM.

AM you're ok, 75Mhz FM - won't work.