What all do you want it to do? Commercial flag, transcode recordings, etc? Will it also be a frontend? I have an older Zotac Mag (ion - HDND01) that I use as small HD frontend, I just ordered a a slightly newer one (ZBOX-ID80-U) that I will use as a HD frontend/slave backend - (I'm giving it 2GB of RAM and attach an external drive - you can buy the plus version that has 2GB of RAM and a slightly larger Hard drive for a bit more if you don't want to add it) I have other slave backends that can do the commercial processing, but these are powerful enough to do it and perform as an HD frontend if you are using VDPAU. I have an HD Homerun, and It integrates easily and well with any recent version of myth. I can't imagine using it with the Zotac would be a problem. The new ZBOX I'm getting will be connected to an HD-PVR.
The Zotac mag I currently have is powered by the older Atom 330, and it can decode mpeg-2 HD without VDPAU. I use it for other things too. It's been rock solid. All downtimes have been planned, and I've had an uptimes 428 and 125 days with it, and it's my primary frontend for the family (quiet, small - but runs a little hot to the touch - you can adjust fan settings in BIOS).