The R600 and T300 should have worked. But the R700 indeed are no longer supported. Not sure where you got the firmware from but the release notes have info on the supported versions. But you might have run into an issue going from unsigned to signed firmware. Which might require an intermediate step. To be honest, for residential idea, the "if ain't broken don't fix it" is probably best so rollback was probably the easiest option.
I know that as a tech guy we always want to play with latest and greatest... ;).