I asked My-Laps how this all works, this is their answer.
The older transponders are compatible with the new RC4 decoder. However, the new RC4 Transponders (non-hybrid) are NOT backwards compatible--therefore, the new RC4's will only work on the RC4 decoder. All existing transponders will work on the RC4 decoder.
I do not need the transponder info that bad, I will keep my original AMB transponders. As far as upgrading the decoder we are working at that.
Tom