Again, I'm not speaking of the RFX, I am talking about adding a second final to the radio as the OP inquired. If you would actually read, and not try to sell something, you would see that.
There is an actual mod that involves adding a second final to the radio, not adding some prefabbed circuit to the radio. I inquired about it when I first bought my DX959, and was advised not to have the mod done by a reputable tech.