Greg, My thoughts and prayers for both you and Joyce. I have always believed people in a coma can hear things and be aware of what is going on around them.
Hospice care can be such a blessing. They help you with things that you might not be able to do, and they know what you need. If you have any questions at all, they are a great go-to resource.
Depending on her musical taste, you might want to play music in the background, although if it is heavy metal I think I'd forgo it and play some smooth jazz or light classical instead. Talk to her, too, telling her how much you love her and talk about things you shared. And if you have the strength to, tell her that it is OK for her to leave now.
With care and big hugs,
Fern