I have the WDTV Live and I use Synology. You can probably get the 712+ cheap for $299 on Newegg deals a couple of times.. I have the 412+ which 4 bays.
Plays AVI, MKV, FLV, any type of popular codec directly off the Synology NAS device. It also has PLEX in case you buy the Roku 3 and needed transcoding.
Thank you for the reply. I'll keep an eye out for the synology. The 712+ is probably as high as I want to go $ wise for a diskless setup. I am guessing it will be quite a bit faster than a WD duo but I have seen the 6tb WD live duo on sale for $360-380. I wish I would have bought it back then... just waiting for another deal like that to come around.