I would just want to send a playlist of three items out asynchronously to my friends, so they can listen whenever they want.
I think the point of the experience is to be in sync while listening, rather than just sharing a playlist with friends.
I get the idea of not creating a massive playlist but I think more than three would be good - I wanted to create a downtempo/ambient playlist and had at least seven tracks in mind. I think 7-9 would be a good number.