Here's a forum thread posted by someone who's using a Supermicro Intel C606-based board with dual xeon E5s and 128GB of memory:
http://tonymacx86.com/viewtopic.php?f=169&t=55963
Looks like they had trouble getting the network functional, but everything else worked fine.
32GB of ECC ram compatible with a motherboard like that would only run you $300:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820161...
Apple charges $975 for an upgrade from 6GB to 32GB. Highway robbery.