Ok. Forget the Atom. It is a red herring. It is no longer Plexing.
I have a Synology NAS, a regular i5 desktop PC and the Virgin Superhub all plugged into the same gigabit switch.
I'm running Plex server on the desktop; watching it, the CPU isn't being overly taxed so all the transcoding it's doing shouldn't be the bottleneck.
I'm trying to pick up films on the Amazon Fire TV Stick (mainly because using the phone or tablet as a remote is fricking awesome), connected to the Superhub over wifi.
The drives shouldn't have been spinning down unless they were unused for an hour. I've upped that to two, just to see if that helps. I've also changed the superhub to use 300Mbps instead of the 144Mbps it was on. I've changed it to 5GHz at the same time, because I'm doing Science wrong. (hoping I'll be able to change that back, simply because the Kindle can't connect at that frequency).
I guess I'll just have to watch more films for now and see how it goes... 'tis a hard life I lead