Using a WD TV LIve Hub you can stream content to other WD TV media players or DLNA compatible device. I would recommend using a Livewire instead of wireless, since you will have much better signal.
I am using two SMP’s in a similar configuration to what you are asking. I have one SMP in my living room connected directly to my USB HDD and I have enabled sharing on that drive through the SMP setup menu. On the second unit, I just tell it to connect to the shared HDD from the living room and everything works great. Just have to remember that you can only use the media library feature on one SMP since enabling it on more than one will corrupt the media library database for both SMP’s.