Ok. Have decided I'm not too fussed about removable storage now. I was going to get the DLINK 320L, but am unsure as to whether it runs wirelessly for the entire household.
From the first user review.
This device is a dock for external hard drives which you connect to a router with an ethernet cable, so that you can access the drives over a network or over the internet. It has two special slots which accept only Seagate GoFlex portable drives, and one standard USB 2.0 port to which you can attach any external drive (of any brand) provided it has a USB connection. There are also two LED gauges which show how full the drives are, but these only work with drives inserted into the GoFlex proprietary slots.
Looks like the two docking slots only work with GoFlex drives. The USB port which can accept a standard usb hard drive is only USB 2 which means transfer speeds will be really slow, although this wouldn't matter for music streaming.
I would avoid as I'm pretty certain with a little research you will find loads of NAS enclosures that could do what you want.