Hardware failures are inescapable over time (the system's about five years old). The good news is that the HD's (three, in a RAID array) are fully functional and all OS' and programs are capable of running and, according to the tech guys, no lost data. So there's that.
Looking for a compatible m-board replacement or, worst case, building an upgraded system using whatever can be repurposed from the original Main System. In the meantime, the laptop, netbook and iPad stand in. God, I hate technology.