FRsky uses the ACCST radio protocol, Spektrum uses DSMX. You are trying to play a Blu-ray in a DVD machine. I would have said VHS in a Betamax machine but nobody would understand me...
You need an FRsky receiver. You want a V8R4 II or V8FR II. First one is 4ch, second one is 8. The S6R is the stabilised FRsky one.