MODULES MUST BE ORDERED AND INSTALLED IN PAIRS for Dual Channel mode. Kingston offers "K2" kit part numbers for Dual Channel mode.
Per Tyan, only slots DIMM 1 & 2 and DIMM 5 & 6 support Dual Rank memory (four ranks total per memory channel). To achieve 32GB using DDR2-667, eight 4GB Single Rank DIMMs must be installed.
Mixing x4 and x8 modules is allowed, however not within the same bank.