Just grabbed on Ebay a Dell Optiplex FX160 for 55€. I got it with stand, power supply, caddy to add a full 2.5 HDD/SSD (alone circa 40€), 2 GB of RAM and a 2 GB flash module. It is powered by an Atom 330 (dual core @ 1.6 GHz with Hyper Threading) with a TDP of only 8 W. I found it interesting because of the full HDD option, the possibility to use a SSD DOM to install the OS, small package and no-fan concept. Below an image of the motherboard:
In the top left corner you can see the port for the flash module (I found in other forums that you may install a bigger DOM SSD), a mini PCI-E port for a Wlan card (it seems that nothing else can be plugged there, at least not with some BIOS modding) and a full Sata port (in blue). Power for the HDD is provided by the white-colored connector next to the PCI-E port. I am currently using a usff PC with a Core 2 Duo E6550 inside. Although my current system performs really well, I wouldn't mind giving this little PC a shot and see how it performs. The lower power consumption is really appealing.
My main concern is the Atom 330. Although it is newer than the E6550, I am not really sure if it has the required muscle (E6550: 2 cores/2 threads @ 2,3 GHz and 65 W TDP; Atom 330: 2 cores/4 threads @ 1,6 GHz and 8 W TDP). I use my OMV mainly as Samba/Printer server and Plex media server to stream content to my Chromecast. I've never seen my OMV transcoding videos for the Chromecast (almost all of them are H.264), and audio streaming does not seem to stress the CPU.
Does anybody have experience with the Atom 330? Does anybody have used such a system (or a similar one) for OMV? I'll update the post as soon as I get the computer and fiddle a little with it.