I'm sure there are other ways of doing this but this is my setup. It kindof assumes that you are only caring about media on the NAS and not just random files.
PS3 Media Server installed on one of the windows machines(one that is on all the time preferred)
uPnPPlay for the app on your prime(and android phone I assume)
I don't know how your windows machines are accessing the NAS. If it is using Samba(or some sort of windows sharing), I think there are a few Samba clients out there for android. I never got these to work as well as I was hoping and I already had the PS3 media server up and running for other devices on my network.