For the Horizon birds, you would need a JR Spektrum tx, at least the 6i or better. At east this way you can run the new DSM2 2.4 and the old DSM1 2.4 version of Spektrum.
As you have found out the 2.4 systems are pretty proprietary, as in you cant use one manufacturers tx with another manufactures rx.

If you go Spektrum or Futaba or Hitec, etc, you'll have t stick with their rx's. Other then Spektrum, as Hobby King now offers a Spektrum clone.