I'm sort of in the same boat here... no son though (phew!). I've been told two different Spektrum options, SPM1014 and SPM1015. I think they are both the Spektrum "pro" series module and receiver but I think the SPM1015 is the HRS module (which I've also been told will NOT work with the SR3500 micro receiver in the HRS mode). If anyone can verify or debunk me I'd appreciate the info.