For me, being diagnosed with DID took a whole slew of psychological tests and an interview with someone who specialized in trauma. Since then, the diagnosis has been confirmed by 2 psychologists with experience with DID. So as someone already said, it would be just wrong for any of us to assign such an extreme diagnosis. But I can share my experience.
For me, I don't experience my parts as voices. Before I started therapy, I would just be one part. The parts were mostly unaware of each other, although I did learn about the "inner child" that we are all supposed to have and could relate, somewhat. But my parts come with feelings (often very strong ones) and actions that differ from part to part. Some dress in a certain way or prefer certain activities. Even now, with some co-awareness of my parts, I don't just hear their voices-I feel their feelings. As an example, today I was upset at my therapist. My "self" was aware that a strong protective part was in charge. I know that more from how my body feels when she is in charge. My body and my mind feel different when she is in charge; kind of hard and pushing people away and suspicious. I do now (after many years of therapy) have times where two or more parts will have opinions and feelings about stuff, but as I said there is always a strong feelings component. So it is not just hearing.