'진짜?' '정말?' '그래요?' are used when you want to assure yourself of what the other say. it sounds like you're not sure that what they talk about really happens. but it can also be a kind of hearing skill.(pretending to agree enthusiastically with the other person) that is to say, if you want to know whether what they say is true or not, you can ask again with 진짜? 정말? 그래요? but you need to be careful of one thing when using them. '진짜?' '정말?' are used between friends, but' 그래요?' is used when you are with your elders. and in the declarative sentences, you can use '진짜, 정말' to emphasize something. but, in this case, you can't use '그래요' because if '그래요' is used in the declarative sentence, it doesn't function as a emphasis. ;)

Both words are interchangeable. Their meaning is almost the same. 저는 정말 음악을 좋아해요. 저는 진짜 음악을 좋아해요.