When I first got my HD500 I was able to play along with music through my headphones connected to the phones jack.  I haven't touched the POD for about 11 months and just now am reaquainting myself with it (had a baby).  Now I just tried to jam along with some songs and I'm unable to do it again.  What am I missing here.  All I want to do is play to a song via iTunes through the HD500.  All drivers and software is up to date.  Please help.  Thanks.