Originally, only 8GB DIMM's were supported.  BIOS version 1.1.4 added support for 16GB DIMM's:[URL]   
This document indicates the max DIMM the Dell R610 can accept is 8GB:  [URL] (page 116)  This document says it can accept DIMMs up to 16GB: www.dell.com/downloads/.../server-poweredge-r610-specs-en.pdf (page 2)  So is it 96GB or 192GB? Maybe a BIOS reflash is needed to get it up to 192GB?   
R610 Max Memory - What is it? Conflicting documentation...