Windows 8 (not RT) is open to you adding apps that share your media if the stock ones don't.
However the Windows Phone 8 as I see it is not so open.
So this means you might want to look at various music/media servers on the PC such as XBMC which I see is out on the Microsoft Store. I don't use that but it's a start.
Xbox Music and Nokia Music both do not collect all of my music in my music folder. I cannot stream all of my music from my PC to other devices except for the hit or miss music Win 8 decides to make available. Unless I pay $9.99 a month.
Does anyone know of a way to stream music on my PC to my Win 8 Phone for free?