Yes, using only riser A(A,C,E,G)on each CPU is a supported configuration. 
Hi all,   I'm looking forward to upgrade R910 servers. Currently it has 4 CPU (Xeon X7560) and each Processor RAM bank have 4 sticks of x 8GB DDR3 (SingleRank). Thus total 128GB of RAM. Current RAM population/config are like this [IMAGE] I would like to add on 4 stick of 32GB DDR3 (Quad rank) to double up the memory from 128GB to 256GB. Need Dell Expert to advise for the config. Thanks!    
R910 RAM Config